Sudden death due to right ventricular cardiomyopathy. A 21-year-old man died suddenly at a small party. He had had no clinical signs of cardiac disease except for a slightly abnormal electrocardiogram (occasional premature ventricular contractions) since he was 15 years of age. Autopsy examination revealed cardiomegaly (469 g), with right atrial and ventricular dilatation. The right ventricular myocardium was massively replaced with adipose tissue, and there was one isolated fatty lesion in the right side of the ventricular septum. There were no congenital malformations such as a septal defect or valvular deformity. Histologically, muscular fibers remaining in the right ventricular wall showed neither degenerative nor inflammatory changes. An isolated lesion of the ventricular septum consisted of almost complete replacement of the muscle bundles with adipose tissue. Such a pathologic condition has recently been termed right ventricular cardiomyopathy. Postmortem examination is necessary to make a definite diagnosis of the disease, because in most adult cases of the disease, sudden death occurs before there have been any critical signs. 