Hypertrophic cardiomyopathy (HCM) is a primary and usually familial cardiac disorder with heterogeneous expression, unique pathophysiology, and a diverse clinical course. Clinically, HCM requires a hypertrophied non-dilated left ventricle without evidence of any other cardiac or systemic disease that could produce the extent of hypertrophy observed. In the vast majority of individual adults dying from HCM, there is cardiomegaly typically in the range of twice the normal heart weight. The characteristic histological features in HCM include the presence of marked myocyte hypertrophy, myofiber disarray, left ventricular outflow tract plaque, intramural coronary abnormalities, and interstitial fibrosis. The pathophysiology of HCM is complex and consists of multiple interrelated abnormalities, including left ventricular outflow tract obstruction, diastolic dysfunction, mitral regurgitation, myocardial ischemia, and arrhythmia. Sudden death is one of the most feared complications of HCM and can be precipitated by physical exercise. The frequency of sudden death in HCM is up to 1% per year in adults with 2 to 4% per year in children and adolescents (McKenna WJ, Behr ER, Heart 87(2):169–76, 2002).