A favorite choice for presentation at clinical pathological conferences is the case of sudden death or terminal congestive heart failure attributed to myocardial hypertrophy of unknown cause. The adjective "idiopathic" affixed to this syndrome merely places a label upon ignorance. Although recent reports have not provided an answer regarding etiologic factors, they have established a readily identifiable clinical state. This disease usually occurs in the second and third decades and is often characterized by dyspnea, syncopal attacks, and electrocardiographic abnormalities which appear early in the illness. There is roentgenographic evidence of generalized cardiac enlargement, and apical murmurs or those at the left sternal border are common. Autopsies have revealed myocardial hypertrophy and fibrosis with normal values. Paré and associates1studied 77 persons in a family in which 50% of the children of any affected member had heart disease. Recognizing that cardiac hypertrophy has been reported to show a familial