Many people first notice hypertrophic cardiomyopathy (HCM) when they feel unexplained shortness of breath, chest pain, a racing or pounding heartbeat, or they faint during exercise or stress; others discover it after a routine check finds a heart murmur or abnormal ECG. In families with HCM, the first signs of hypertrophic cardiomyopathy 4 often surface when a relative is diagnosed and others get screened, sometimes revealing the condition before symptoms start. In teens and young adults, how hypertrophic cardiomyopathy is first noticed can be a sudden episode—like fainting on the field—or gradual clues like reduced exercise tolerance, dizziness, or palpitations that prompt a cardiac evaluation.