a familial condition affecting the heart, characterized by unexplained thickening (hypertrophy) of the wall of the left ventricle. In many cases this is an incidental finding and patients have a good outcome. However, more severely affected patients may suffer chest pain, tachyarrhythmia (see arrhythmia), heart failure, and sudden death. In some cases there is focal thickening of muscle around the left ventricular outflow tract (asymmetric septal hypertrophy, ASH), and this can result in restriction of blood flow to the body (hypertrophic obstructive cardiomyopathy, HOCM). The diagnosis is made by electrocardiography, echocardiography, and cardiac *magnetic resonance imaging. Usually drug treatment is sufficient to control symptoms, but some patients require cardiac *catheterization or surgical treatment. Those deemed at highest risk of sudden death may require an *implantable cardiovertor defibrillator.