In 46 patients with aortic valve disease, coronary sinus blood flow was measured using a continuous thermodilution method both at rest and during isometric handgrip exercise. All patients had normal coronary angiograms. The patients were separated into three groups: Group I, 12 patients with aortic stenosis (systolic gradient 72 +/- 12 mm Hg); Group II, 15 patients with both aortic stenosis and regurgitation; Group III, 19 patients with aortic regurgitation. At rest, the coronary sinus blood flow was two to three times normal. However, when corrected for left ventricular mass (ml/100 g), flow was within normal limits. The ratio diastolic pressure-time index/systolic pressure-time index (DPTI/SPTI) was decreased in all three groups at rest. During isometric exercise, coronary sinus blood flow increased significantly: by 60 percent in Group I, by 88 percent in Group II and by 118 percent in Group III. There was a significant reduction of the DPTI/SPTI ratio. Of the 18 patients with angina on effort during the test, 7 were in Group I, 6 in Group II and 5 in Group III. There were no differences in the coronary sinus blood flow between the patients with angina and those who were pain-free, either at rest or during exercise. Angina pectoris does not appear to be caused by a failure of coronary blood flow to increase. There was no discrepancy between myocardial demand, as measured by the pressure-time index and coronary blood flow. However, the DPTI/SPTI ratio was significantly lower during exercise in the patients with angina than in those who were pain-free. Underperfusion of the subendocardial muscle seems to be a causative factor in the patients with angina.