This report details the clinical, hemodynamic, and morphologic data from four patients 59 to 77 years old (mean 66) with a primary restrictive cardiomyopathy. All patients had symptoms of congestive heart failure, jugular venous distention, and murmurs of mitral and tricuspid regurgitation. Four patients required pacemakers, three for the brady-tachy syndrome and one for complete heart block. Chest x-ray demonstrated cardiomegaly in all four patients and pulmonary congestion and/or pleural effusions in three. Echocardiographic examination documented left atrial enlargement in all patients, along with normal left ventricular internal dimensions. Global left ventricular systolic function was normal in all, and left and right ventricular filling pressures were elevated and similar in three. A dip and plateau pattern was present in the pressure tracings of two of three patients. Unlike previous reports of restrictive cardiomyopathy, in our four patients there was no specific morphologic cause noted at necropsy. Pathologic evaluation demonstrated biatrial dilatation in all patients, with thrombi present in the atrial appendages in three. Normal ventricular cavity size and mild right ventricular hypertrophy were present in all patients and mild-to-moderate left ventricular hypertrophy was present in two. There were no significant pericardial, endocardial, or valvular abnormalities and no infiltrative myocardial disorders were present. Light and electron microscopic studies demonstrated only interstitial fibrosis of the myocardium. A restrictive hemodynamic profile may be observed in the absence of specific infiltrative disorders and affected patients may exhibit a prolonged clinical course of 4 to 14 years (mean 9). However, in these patients congestive heart failure responded poorly to medical therapy or surgical correction of valvular regurgitation, which is common in this disorder.