Above. Hypertrophic cardiomyopathy (HCM) is defined as a myocardium (heart muscle) which becomes hypertrophied (enlarged) often without a demonstrable cause. Hereditary factors may play a role since over half of the patients have a first degree relative with the disease. HCM may become apparent during adolescence and young adulthood. The ventricular cavity may either be normal or small, and congestive heart failure may occur due to impaired left ventricular performance.