Third-degree atrioventricular block is a serious heart rhythm problem where electrical signals do not travel from the upper chambers of the heart to the lower chambers. It can cause severe tiredness, dizziness, fainting, shortness of breath, or chest discomfort, and the early symptoms of third-degree atrioventricular block can be easy to miss at first. It most often affects older adults or people with heart disease, but it can also happen after a heart attack, with certain medicines, or from a heart condition present at birth. Not everyone will have the same experience. Third-degree atrioventricular block usually needs urgent treatment, often with a pacemaker, because without treatment it can lead to injury from fainting, heart failure, or death.
How many people live with Third-degree atrioventricular block?
Based on the widely cited estimate that third-degree atrioventricular block, also called complete heart block, affects about 0.02% to 0.04% of people overall, roughly 1.6 to 3.2 million people may be living with it worldwide (StatPearls, 2023). Using that same prevalence range, the U.S. estimate is about 67,000 to 134,000 people (StatPearls, 2023), but these are rough estimates rather than direct counts because published numbers vary and often come from study groups instead of whole-population tracking.
Overview
Third-degree atrioventricular blockSymptoms
Third-degree atrioventricular block can cause extreme tiredness, dizziness, fainting, chest discomfort, or shortness of breath. Many people notice a very slow heartbeat. In severe cases, it can cause confusion or collapse.
Outlook and prognosis
With third-degree atrioventricular block, outlook is often good when treatment restores a steady heartbeat, usually with a pacemaker. Without treatment, fainting, heart failure, or sudden cardiac arrest can happen. Prognosis also depends on the underlying heart problem.
Causes and risk factors
Third-degree atrioventricular block can result from aging-related electrical system damage, heart attack, heart surgery, or medicines that slow conduction. Risk is higher with coronary artery disease, inflammation, infections, and some congenital heart conditions. Rarely, it is present from birth.
Genetic influences
Genetics can matter in third-degree atrioventricular block, but many cases are not inherited. Some people have gene changes that affect the heart’s electrical system, especially when this starts young or runs in families.
Diagnosis
Third-degree atrioventricular block is usually diagnosed with an electrocardiogram, which shows the heart's electrical signals are not traveling normally between the upper and lower chambers. Doctors may also use heart monitoring, blood tests, and imaging to look for a cause.
Treatment and drugs
Third-degree atrioventricular block usually needs urgent treatment because the heart’s electrical signals are fully blocked. Many people with third-degree atrioventricular block need a pacemaker to keep the heartbeat steady. Doctors also treat any reversible cause, such as medication effects or low potassium.
Symptoms
Third-degree atrioventricular block can make everyday activity feel suddenly harder, with spells of dizziness, exhaustion, or feeling close to passing out. This happens because the heart is beating too slowly or out of sync, so less blood reaches the brain and body. Symptoms vary from person to person and can change over time. Some people have mild warning signs at first, while others develop severe symptoms that need urgent medical care.
One of the early symptoms of third-degree atrioventricular block can be feeling lightheaded, woozy, or unsteady, especially when you stand up or exert yourself. Some people also notice dim vision or a sudden need to sit or lie down.
If the heart slows too much, you may briefly lose consciousness or nearly pass out. Even a short blackout can be a warning sign that needs urgent medical attention.
Many living with third-degree atrioventricular block feel unusually tired or weak because the body is not getting enough blood flow. What once felt effortless can start to require more energy or focus.
Shortness of breath can happen during walking, climbing stairs, or other routine activity, and sometimes even at rest. Day to day, it can feel like needing to stop and catch your breath during tasks that used to be manageable.
How people usually first notice Third-degree atrioventricular block?
People usually first notice third-degree atrioventricular block when the heartbeat becomes so slow or unreliable that everyday activities suddenly feel harder, with unusual fatigue, dizziness, fainting, shortness of breath, or a sense that the heart is skipping or beating too slowly. Some people with third-degree atrioventricular block first realize something is wrong during exertion, while others are picked up after a collapse, chest discomfort, confusion, or a doctor finding a very low pulse on an exam. In some cases there are few warning signs until it is seen on an electrocardiogram, which is why new fainting, near-fainting, or unexplained weakness should be checked promptly.
Types of Third-degree atrioventricular block
Third-degree atrioventricular block, also called complete heart block, is not always exactly the same from one person to another. Doctors usually describe the types of third-degree atrioventricular block by when it starts and by where the heart’s backup rhythm comes from, because those differences can affect symptoms and urgency. Some people feel only tired or lightheaded, while others may faint or become short of breath with very little activity. Symptoms don’t always look the same for everyone.
Congenital block
This form is present at birth, and some people living with it have few symptoms for years because the heart develops a steady backup rhythm. Others may notice poor exercise tolerance, unusual fatigue, or dizziness, especially during growth, illness, or pregnancy.
Acquired block
This type develops later in life, often from heart disease, aging of the electrical system, a heart attack, or certain medicines. Symptoms are often more sudden and can include marked tiredness, fainting, chest discomfort, or shortness of breath.
Junctional escape
In this pattern, the backup heartbeat starts higher up in the electrical system, near the atrioventricular node. The heart rate is usually slow but often less extreme, so symptoms may be milder, such as fatigue, reduced stamina, or occasional lightheadedness.
Ventricular escape
Here, the backup rhythm starts lower down in the ventricles, which usually makes the heart beat much more slowly and less reliably. Many with this form have more severe symptoms, including near-fainting, fainting, weakness, confusion, or trouble breathing, and it is more likely to need urgent treatment.
Can I slow down the onset of symptoms?
Usually not: there is no strong evidence that lifestyle changes can meaningfully delay the start of symptoms from third-degree atrioventricular block, also called complete heart block, because it often happens when the heart’s electrical pathway becomes damaged by age, heart disease, certain medicines, infection, or heart surgery. Healthy habits like not smoking, staying active, getting enough sleep, and keeping blood pressure, cholesterol, diabetes, and sleep apnea under good control may support overall heart health and may lower some underlying risk, but that is not the same as preventing complete heart block, and research has not shown they reliably delay when it begins. The main medical steps are regular follow-up if you are at risk, reviewing medicines that can slow the heartbeat, and treating fixable causes early; if complete heart block develops, a pacemaker is the standard treatment, so early care can still make a real difference even if it cannot promise prevention.
What genetics can tell you about symptoms
Genetics can sometimes help explain why third-degree atrioventricular block shows up earlier in life, runs in families, or comes with other heart problems, but in many people it is not caused by a single inherited change. Certain genetic variations linked to the heart’s electrical system can affect how severely the signal between the upper and lower chambers is slowed or blocked, which may influence symptoms such as fatigue, dizziness, fainting, or a very slow heartbeat and may also raise the chance of developing related rhythm problems. Even so, genes usually cannot predict the exact symptoms one person will have, because age, underlying heart disease, medicines, and other health factors also play a big role.
Causes and risk factors
After a heart attack or heart surgery, some people start having dizziness or fainting because the heart’s electrical pathway has been damaged. Third-degree atrioventricular block can also develop from aging, heart inflammation, or scarring. Some risks are modifiable (things you can change), others are non-modifiable (things you can’t). Infections such as Lyme disease, high potassium levels, and medicines that slow the heartbeat too much are important risk factors for third-degree atrioventricular block. Rarely, babies are born with it because of a heart defect, an inherited rhythm condition, or immune proteins from the mother during pregnancy, and smoking, heavy alcohol use, and stimulant drugs can add to the risk.
What are the most common causes or risk factors?
Third-degree atrioventricular block, also called complete heart block, is most often caused by aging-related scarring in the heart’s electrical system, heart disease such as a past heart attack, or damage after heart surgery or certain heart procedures. It can also be triggered by medicines that slow the heart’s electrical signals, including some beta blockers, calcium channel blockers, and digoxin, and less often by infections or inflammation that affect the heart, such as Lyme disease or myocarditis. Some people are born with it, and in rare cases it is linked to inherited heart conditions or to immune proteins from a mother with an autoimmune disease, such as lupus, affecting the baby during pregnancy.
Environmental and biological risk factors
Third-degree atrioventricular block, also called complete heart block, happens when electrical signals from the top chambers of the heart no longer reach the bottom chambers. The common causes of third-degree atrioventricular block range from age-related changes in the heart's wiring to heart damage, inflammation, medicines, and some medical procedures. Doctors often group risks into internal (biological) and external (environmental).
With aging, the heart’s electrical pathways can gradually become scarred or worn, making signal transfer less reliable. This is one of the most common biological risk factors for third-degree atrioventricular block in older adults.
A heart attack, especially one affecting the lower part of the heart, can injure the atrioventricular node or nearby tissue. When that damage is severe, signals may stop reaching the lower chambers.
Existing heart disease, such as cardiomyopathy, valve disease, or heart failure, can stretch, scar, or distort the tissue that carries electrical signals. Many living with third-degree atrioventricular block have an underlying structural heart problem.
Inflammation of the heart from conditions such as myocarditis, Lyme disease, or other infections can disrupt the heart’s wiring. Sometimes the block improves when the underlying cause is treated, but not always.
Genetic risk factors
For some families, third-degree atrioventricular block is linked to an inherited problem in the heart’s electrical system rather than a random event. When doctors look into the genetic causes of third-degree atrioventricular block, they usually focus on family history, gene changes that slow electrical signals, and inherited heart or muscle conditions. Carrying a genetic change does not guarantee the condition will appear, but it can raise the chance of developing it or of getting it at a younger age.
Family history: A close relative with complete heart block, unexplained fainting, a pacemaker at a young age, or sudden cardiac death can be a clue that risk runs in the family. This does not prove a genetic cause, but it makes inherited testing and a specialist heart review more important.
SCN5A changes: Changes in SCN5A can slow the electrical signal as it moves from the upper to lower chambers of the heart. In some families, this causes a progressive conduction problem that can lead to third-degree atrioventricular block.
LMNA changes: Changes in LMNA can affect both the heart muscle and its electrical wiring. Many living with LMNA-related disease develop conduction problems early, and some later progress to third-degree atrioventricular block.
Heart development genes: Some inherited gene changes, especially in NKX2-5, affect how the heart forms before birth and how its electrical pathways develop. People with these changes may have a heart defect at birth, a slow heartbeat, or later develop complete heart block.
Inherited cardiomyopathy: Some gene changes that cause a weakened, enlarged, or thickened heart also disturb the pathways that carry electrical signals. This can raise the risk of worsening atrioventricular block, including third-degree atrioventricular block, over time.
Muscle-linked disorders: Inherited conditions that affect muscles and nerves, such as myotonic dystrophy, can also involve the heart’s electrical system. Some people develop slowly worsening conduction problems that eventually reach third-degree atrioventricular block.
Lifestyle risk factors
Third-degree atrioventricular block is usually caused by damage or disease in the heart’s electrical system rather than by lifestyle habits alone. Still, how lifestyle affects third-degree atrioventricular block matters because certain habits, substances, and daily patterns can worsen symptoms, trigger dangerous slow heart rates, or increase complications around an already fragile rhythm. The main lifestyle risk factors for third-degree atrioventricular block are those that strain the heart, promote underlying heart disease, or interfere with conduction.
Smoking damages blood vessels and raises the risk of coronary artery disease, which can injure the conduction system and make complete heart block more likely or more unstable. It also lowers oxygen delivery and can worsen chest pain, fatigue, and fainting in people who already have severe bradycardia.
Heavy alcohol use can weaken heart muscle, trigger rhythm problems, and worsen the cardiac disease that sometimes accompanies third-degree atrioventricular block. In someone with established block, excess alcohol may increase dizziness, falls, and poor blood pressure control.
Cocaine, amphetamines, and other recreational drugs can stress the heart, provoke ischemia, and worsen electrical instability. Even when they do not directly cause complete block, they can make symptoms and complications more dangerous.
Taking more than prescribed of drugs that slow conduction, such as some β-blockers, calcium channel blockers, or digoxin, can worsen bradycardia and unmask severe block. Using supplements or over-the-counter products without checking for interactions can add to this risk.
Risk prevention
Third-degree atrioventricular block cannot always be prevented, because it may happen with aging, heart disease, certain medicines, or less often from birth. In many people, prevention means lowering the risk of the heart problems that can lead to it and catching rhythm changes early before they become dangerous. Prevention works best when combined with regular check-ups.
Managing high blood pressure, coronary artery disease, and heart failure can lower the risk of damage to the heart’s electrical system. For many living with third-degree atrioventricular block, this is one of the most important ways to reduce preventable worsening.
Some medicines can slow electrical signals in the heart, including certain beta blockers, calcium channel blockers, digoxin, and some antiarrhythmics. Never stop a prescription on your own, but ask your doctor whether any medicine could raise your risk of third-degree atrioventricular block.
A few infections and inflammatory illnesses can injure the heart and trigger serious rhythm problems. Getting timely care for chest pain, fever with new palpitations, or unexplained fainting may help prevent complications related to third-degree atrioventricular block.
Low or high potassium and other mineral imbalances can interfere with normal heart conduction. Regular blood tests may be important if you have kidney disease, take water pills, or have vomiting or diarrhea.
Can you prevent Third-degree atrioventricular block?
You usually cannot fully prevent third-degree atrioventricular block, a severe form of heart block, because it often happens from aging-related changes in the heart’s electrical system, heart damage, or conditions present from birth. Some risk may be lowered by treating heart disease early, managing blood pressure and diabetes, not smoking, and having your medicines checked if any can slow the heart’s electrical signals.
Transmission
Third-degree atrioventricular block is not contagious, and it is not infectious at all. You cannot catch it from another person through touch, coughing, sex, food, or everyday contact.
If you are wondering how third-degree atrioventricular block is inherited, most cases are not passed directly from parent to child. Some babies are born with it, and a small number of cases are linked to inherited heart conditions or to antibodies from the pregnant parent crossing the placenta during pregnancy.
When to test your genes
Genetic testing is not routine for most people with third-degree atrioventricular block, because it is often caused by aging, heart disease, medications, or other acquired problems. It becomes more useful if the block appears at a young age, runs in your family, or comes with cardiomyopathy, muscle disease, or sudden unexplained deaths.
Diagnosis
Third-degree atrioventricular block is usually diagnosed when symptoms like fainting, unusual tiredness, shortness of breath, or a very slow pulse lead to urgent medical evaluation. In day-to-day life, this can look like getting lightheaded while walking across a room or needing to sit down after mild activity. It’s natural to worry when symptoms don’t have a clear explanation. Doctors confirm the diagnosis of third-degree atrioventricular block by checking the heart’s electrical pattern and looking for the cause.
Doctors ask about symptoms such as fainting, dizziness, chest discomfort, palpitations, or trouble keeping up with usual activities. They also review medicines, past heart disease, infections, and whether symptoms came on suddenly or gradually.
A clinician checks your pulse, blood pressure, and signs that the heart is beating too slowly to meet the body’s needs. They may also listen for heart sounds and look for clues of heart failure or poor blood flow.
An ECG is the main test used to diagnose third-degree atrioventricular block. It shows that the upper and lower chambers are beating independently, which confirms a complete block in electrical signaling.
If the block is not captured on a standard ECG, doctors may use continuous hospital monitoring, a Holter monitor, or an event recorder. These tests help link symptoms with brief or intermittent episodes of abnormal rhythm.
How is Third-degree atrioventricular block diagnosed?
Third-degree atrioventricular block, also called complete heart block, is usually diagnosed with an electrocardiogram, or ECG/EKG, a simple heart tracing that shows the upper and lower chambers beating out of sync because the electrical signal is not getting through. If it does not happen all the time, doctors may use a portable heart monitor worn for a day or longer, and they may also do blood tests and heart imaging to look for a cause. Genetic testing is not usually needed to diagnose the block itself, but it may be considered if there are signs of an inherited heart condition or a strong family history.
Stages of Third-degree atrioventricular block
Third-degree atrioventricular block does not have defined progression stages. That is because it is usually identified as a specific heart rhythm problem on an electrocardiogram, rather than a condition that moves through clear step-by-step phases over time. Some people are diagnosed suddenly when early symptoms of third-degree atrioventricular block, such as fainting, severe dizziness, or unusual tiredness, bring them to urgent care, while others are found during testing for a very slow pulse. Doctors usually start with a conversation about symptoms and medical history, then confirm the diagnosis with heart rhythm tests such as an ECG and sometimes longer monitoring.
Outlook and prognosis
The outlook for third-degree atrioventricular block depends greatly on the cause, the speed of diagnosis, and whether a pacemaker is implanted promptly. Without treatment, complete heart block can cause severe fatigue, fainting, heart failure, dangerous low heart rates, and sudden cardiac death, so the mortality risk is significantly increased. In contrast, most people who receive timely pacing have a much better prognosis, with major improvement in symptoms and a substantial reduction in life-threatening complications. Long-term outcome is also shaped by any underlying heart disease, such as prior heart attack, cardiomyopathy, or congenital heart conditions. Some temporary cases related to medications, electrolyte problems, or acute illness may improve if the trigger is reversed, but persistent complete block usually requires lifelong follow-up and permanent pacing.
Long-term effects
Third-degree atrioventricular block can have serious long-term effects because the signal between the upper and lower chambers of the heart is fully interrupted. This can leave the heart beating too slowly to meet the body’s needs, especially during activity or illness. Thinking about the long-term effects helps explain why this condition usually needs urgent treatment and close follow-up. With a pacemaker, many people do much better, but the outlook still depends on the cause, age, and overall heart health.
A very slow heart rate can cause lasting tiredness, weakness, and poor stamina in daily life. Some people with third-degree atrioventricular block find that walking stairs, shopping, or even standing up for long can become much harder.
Reduced blood flow to the brain can lead to dizziness, near-fainting, or sudden fainting. These episodes raise the risk of falls, fractures, and driving accidents, and they may be one of the early symptoms of third-degree atrioventricular block.
When the heart cannot keep a steady, effective rhythm, it may struggle to pump enough blood over time. This can lead to shortness of breath, swelling in the legs, and fluid buildup, especially in people who already have heart disease.
Long-term low blood flow can affect how well the kidneys, brain, and other organs work. Many living with untreated complete heart block may notice confusion, worsening fatigue, or less ability to cope with exercise or illness.
How is it to live with Third-degree atrioventricular block?
Living with third-degree atrioventricular block can feel unsettling because the heart’s upper and lower chambers are no longer coordinating, so many people live with fatigue, dizziness, shortness of breath, or fainting that can make driving, exercise, work, and even routine errands feel less predictable. For many, daily life becomes much steadier after treatment, most often with a pacemaker, but it can still mean planning around medical visits, watching for symptoms, and taking extra care with activities where a sudden blackout could put you at risk. It also affects the people around you, who may need to help in an emergency, drive you to appointments, or adapt family and work routines while treatment is being arranged, yet with proper care many people are able to return to a safer and more active life.
Treatment and drugs
Third-degree atrioventricular block is treated by restoring a safe, steady heartbeat, because the heart’s upper and lower chambers are no longer working in sync. In urgent situations, doctors may use medicines for a short time or place a temporary pacemaker, which is a device that sends electrical signals to keep the heart beating until a longer-term plan is in place. For many people living with third-degree atrioventricular block, the main treatment is a permanent pacemaker placed under the skin of the chest to prevent slow heart rates, fainting, tiredness, and other symptoms. Treatment plans often combine several approaches, so doctors also look for and treat causes such as medication side effects, heart damage, infection, or problems with body salts like potassium.
Can you cure Third-degree atrioventricular block?
Third-degree atrioventricular block, also called complete heart block, usually is not something that can be cured with medicine alone. If it is caused by a temporary problem, such as a drug side effect or another illness, treating that cause may reverse it, but many people need a pacemaker to keep the heart beating in a safe, steady way. Treatment can work very well to control the condition and lower the risk of fainting, shortness of breath, or other serious heart problems.
Non-drug treatment
Third-degree atrioventricular block can make everyday life feel unsteady, with sudden dizziness, fainting, extreme tiredness, or shortness of breath because the heart is beating too slowly. Non-drug treatments may be recommended urgently, since this rhythm problem often needs electrical support rather than watchful waiting. For many living with third-degree atrioventricular block, the main treatment is a pacemaker, along with monitoring and practical safety steps while care is being arranged.
In urgent settings, doctors may use external pads or a wire placed through a vein to keep the heart beating at a safer rate. This can stabilize blood flow and reduce fainting, chest discomfort, or severe weakness while a longer-term plan is made.
A permanent pacemaker is the main long-term treatment for third-degree atrioventricular block. It sends small electrical signals to keep the heart rhythm steady, which often improves symptoms and is central to treatment for third-degree atrioventricular block.
Many people need hospital monitoring at first, especially if symptoms started suddenly or the heart rate is very low. Continuous heart tracing helps the team see how often the block happens, how severe it is, and when pacing is needed.
If the block is linked to another heart problem, treatment may also involve procedures that address that cause, such as care around heart surgery or treatment of damaged heart tissue. Not every approach works the same way, because the best plan depends on why the block developed and whether it may improve.
Your genes may have an impact on how drugs work for you
For people living with third-degree atrioventricular block, genes usually matter more in causing the heart’s electrical problem than in changing how most treatments work, because the main treatment is often a pacemaker rather than long-term medicine. Some people with an inherited heart condition may be more sensitive to medicines that slow the heart’s electrical signals, so a drug that is safe for one person can sometimes worsen the block in another. Even so, routine genetic testing to pick medicines is not a standard part of care for this condition, and treatment decisions are usually based more on the heart rhythm, symptoms, and the cause of the block.
Pharmacological treatments
With third-degree atrioventricular block, medicines are usually a short-term bridge rather than the main fix. This heart rhythm problem often needs urgent pacing, especially if it is causing fainting, chest pain, low blood pressure, or severe dizziness. Drug treatments aren’t about fixing everything at once, but they can help raise the heart rate and support blood flow while doctors arrange pacing or treat a reversible cause.
Atropine may be tried first in some emergency settings to help speed the heart rate. It tends to work best when the block is higher up in the heart’s electrical system, so in many people with third-degree atrioventricular block it has little or only brief effect.
Dopamine can be given through a vein to support heart rate and blood pressure when third-degree atrioventricular block is causing poor circulation. It is usually used for close monitoring in the hospital while temporary or permanent pacing is being arranged.
Epinephrine may also be used by IV as a temporary medicine when the heartbeat is dangerously slow. This can be especially important when early symptoms of third-degree atrioventricular block include fainting, marked weakness, confusion, or severe lightheadedness.
Isoproterenol is sometimes used to raise the heart rate when urgent pacing is not immediately available or while a reversible cause is being addressed. Because it can trigger fast or abnormal rhythms, it is generally reserved for carefully monitored situations.
Genetic influences
If a relatively young adult suddenly needs a pacemaker, families often wonder whether third-degree atrioventricular block runs in families. Family history is one of the strongest clues to a genetic influence. Most cases of third-degree atrioventricular block are not caused by a single inherited gene and are more often linked to aging, heart disease, heart surgery, inflammation, or certain medicines. Still, rare inherited gene changes can affect the heart’s electrical pathways or heart muscle and make this kind of block more likely, especially when it appears early in life or along with fainting, heart muscle disease, or other rhythm problems. If several relatives have had unusually slow heart rhythms or needed pacemakers at a young age, doctors may suggest genetic counseling and sometimes genetic testing. That can help clarify whether other family members may benefit from heart rhythm checks.
Is Third-degree atrioventricular block genetic?
Genetics can matter in third-degree atrioventricular block, but many cases are not inherited. Some people have gene changes that affect the heart’s electrical system, especially when this starts young or runs in families.
Having a genetic risk is not necessarily a diagnosis
Genetic variants are a usual part of human biology and are widely found in the general population. Most do not have a direct impact on health and simply represent natural human variation. For many genes, carrying a variant connected with a condition suggests a possible link rather than a certain diagnosis, especially when more than one gene and environmental factors play a part. In some situations, though, a single well-studied variant in a particular gene can be enough to confirm a diagnosis.
Pharmacogenetics—how genetics influence drug effects
When third-degree atrioventricular block causes fainting, severe dizziness, or sudden exhaustion, treatment usually focuses on getting the heart back to a safe rhythm quickly, often with temporary pacing first and then a permanent pacemaker if the block persists. Genetic changes can matter because, in some families, this type of heart block is part of an inherited problem in the heart’s electrical system, and it may worsen over time or come with other dangerous rhythm changes. In that setting, a genetic result can help doctors decide how closely to monitor you, whether relatives should be checked, and whether a device with a defibrillator may be safer than a pacemaker alone. Genetics is only one factor, but it can also affect medication decisions, since drugs that further slow electrical signals in the heart may need to be avoided or used with extra caution in people with third-degree atrioventricular block. This is why genetic testing for third-degree atrioventricular block may be discussed when the condition starts at a younger age, runs in a family, or appears along with an enlarged or weakened heart.
Interactions with other conditions
For many people, third-degree atrioventricular block becomes most noticeable when it overlaps with another heart problem, such as coronary artery disease, a recent heart attack, or heart failure. Someone might notice that walking across the room suddenly brings more dizziness, chest discomfort, or shortness of breath than usual because the heart is beating too slowly to keep up with the body’s needs. Doctors call it comorbidity when two conditions occur together, and in this setting the combined effect can make third-degree atrioventricular block more dangerous and symptoms more intense.
It can also appear with inflammatory or infiltrative illnesses that affect the heart, including myocarditis, sarcoidosis, or amyloidosis, and these conditions may need their own treatment in addition to pacing support. In some people, infections such as Lyme disease can disturb the heart’s electrical system and lead to a severe block, so treating the infection matters as well as treating the rhythm problem. Early symptoms of third-degree atrioventricular block can be harder to spot in older adults or in people already living with fatigue, fainting spells, or exercise intolerance from another illness, which is why a full medical review is important.
How genes can cause diseases
Humans have more than 20,000 genes, each carrying out one or a few specific functions in the body. One gene instructs the body to digest lactose from milk, another tells the body how to build strong bones and another prevents the body's cells from beginning to multiply uncontrollably and developing into cancer. As all of these genes combined are the building instructions for our body, a defect in one of these genes can have severe health consequences.
Through decades of genetic research, we know the genetic code of any healthy/functional human gene. We have also identified that in certain positions on a gene, some individuals may have a different genetic letter from the one you have. We call these hotspots "Genetic Variations" or "Variants" in short. In many cases, studies have been able to show that having the genetic letter "G" in the position makes you healthy, but having the letter "A" in the same position disrupts the gene function and causes a disease. Genopedia allows you to view these variants in genes and summarizes all that we know from scientific research, which genetic letters (Genotype) have good or bad consequences on your health or on your traits.
What other conditions can cause similar symptoms to Third-degree atrioventricular block?
Other slow heart rhythm problems, such as second-degree heart block or a problem with the heart's natural pacemaker, can cause very similar symptoms like dizziness, fainting, unusual tiredness, and shortness of breath. The same symptoms can also happen from medicines that slow the heart, a heart attack, or changes in body salts such as potassium. In some people, low blood pressure or other abnormal heart rhythms can look similar too, so tests are usually needed to tell the cause apart.
History
For many living with third-degree atrioventricular block, the history of this condition helps explain why symptoms like fainting, unusual tiredness, or a very slow heartbeat are taken so seriously today. Long before modern heart monitors existed, doctors noticed that some people would suddenly black out, struggle with exertion, or seem to have a pulse that was much slower than expected for how they felt.
In the 18th and 19th centuries, careful bedside observations began to connect these episodes with problems in the heart’s rhythm rather than with the brain alone. Some of the earliest medical reports described people who had repeated fainting spells because the upper and lower chambers of the heart were no longer beating in step. This was a major step, because it showed that third-degree atrioventricular block was a problem of electrical timing inside the heart.
As medical science evolved, the invention of the electrocardiogram, or ECG, in the early 1900s changed everything. Doctors could now see the heart’s electrical signals on paper and recognize when messages from the upper chambers were not reaching the lower chambers at all. That made diagnosis much more accurate and helped separate third-degree atrioventricular block from other causes of dizziness, collapse, or weakness.
Through the mid-20th century, treatment improved dramatically. Before reliable pacing devices, severe heart block could be life-threatening and often left people with little protection from very slow heart rates. The development of external pacing and then implanted pacemakers transformed care, allowing many people with third-degree atrioventricular block to live longer and more active lives.
Later research showed that complete heart block can happen for different reasons, including age-related changes in the heart’s electrical system, heart disease, certain infections, inflammation, or after some heart procedures. Researchers also learned that, in some families or from birth, there can be an underlying genetic cause, although that part of the story is usually covered separately from the clinical history.
Today, the history of third-degree atrioventricular block is closely tied to advances in heart rhythm medicine. What was once recognized mainly after dramatic fainting episodes can now often be picked up earlier through ECGs, heart monitoring, and evaluation of early symptoms of third-degree atrioventricular block. That progress has made the condition much more understandable and, in many cases, much more treatable than it was in the past.