Cardiac ultrastructure in primary restrictive cardiomyopathy.

A five-year clinical follow-up and the results of myocardial biopsies are described in a patient with primary restrictive cardiomyopathy. Histologic examination of a right ventricular endomyocardial biopsy taken early in the course of the illness was not contributory. Histologic examination of a left ventricular endomyocardial biopsy five years later showed hypertrophy and disarray of myocytes, thickening of the endocardium, and interstitial fibrosis. Connective tissue was compact and regularly oriented in the endocardium, but tangled and irregularly oriented in the interstitium. It is concluded that the irregular network of collagen fibrils and elastic fibers limits diastolic relaxation and prevents ventricular dilatation; that the coexisting hypertrophy results from an attempt to maintain normal pump function; and that the myocyte disarray is a consequence of abnormal mechanical forces generated under conditions of severe fibrosis.