Restrictive cardiomyopathy is uncommon and in its overt form is associated with heart failure, characterized primarily by abnormalities in diastolic function and preserved or nearly preserved systolic function. It may be associated with amyloidosis, hemochromatosis or endomyocardial fibrosis. We describe five patients with restrictive cardiomyopathy, ages ranging from 35 to 71 (mean 49), three of whom were men. Fatigue, dyspnea on exertion and chest pain were the most frequent symptoms. Only one patient had overt heart failure, and three had normal or near-normal hemodynamics at rest that became greatly abnormal with exercise. Four of the five patients are alive now 9 to 77 (mean 33) months following the onset of symptoms. Despite prior emphasis on specific causes, restrictive cardiomyopathy in this series had no definable cause. Moreover, the presence of a "latent" form of restriction (abnormalities only with exercise) suggests that the incidence of the disease may be higher than previously appreciated.