Hypertrophic cardiomyopathy (HCM) is the single most common cause of sudden death in otherwise healthy young people, found in approximately half of such cases. It is a genetic disease occurring in approximately 1 in 500-1,000 of the general population. The myopathy is often undiagnosed and asymptomatic cases are often unrecognised. Usually, HCM develops with progressive asymmetric LV hypertrophy (LVH) during the period of rapid body growth of adolescence, but it may be present in childhood or even before birth. Progressive hypertrophy after age 20 is uncommon, but initial diagnosis even in old age is not. The hypertrophy predominantly involves the LV, and is often more marked than in any other cardiac disease. It represents hypertrophy and hyperplasia of several cell types, including cardiac myocytes, fibroblasts, and smooth muscle cells, along with excessive collagen and matrix deposition. The normal parallel arrangement of myocytes is often disturbed (fibre disarray).