We studied six patients who suffered from angina pectoris but had angiographically patent major coronary arteries. Two of the patients suffered also from congestive heart failure. Three patients had supraventricular tachyarrhythmias. Three patients had conduction disturbances. During coronary angiography the patients had significantly reduced flow velocity of angiographic contrast medium compared with that in a control group. Echocardiographic and Doppler flow studies showed a tendency for symmetrical thickening of the left ventricular wall, enlargement of the right ventricle, and reduced compliance of both ventricles. Right ventricular endomyocardial biopsy revealed pathologic small coronary arteries with fibromuscular hyperplasia, hypertrophy of the media, myointimal proliferation, and endothelial degeneration. Capillaries had swollen endothelial cells encroaching on the lumen. Myocardial hypertrophy, lipofuscin deposition, and patchy fibrosis were also observed. These cases show that small-vessel coronary artery disease can cause classic angina pectoris. The diagnosis can be suspected when the coronary angiogram shows large patent arteries with slow flow of the angiographic contrast medium and it can be confirmed by endomyocardial biopsy.