In a prospective study, 11 (1.5 percent) of 742 patients had angiographically proven coronary artery aneurysms. The clinical picture was similar to that of patients with severe coronary artery disease. The coronary artery aneurysms were multiple and were associated with extensive coronary atherosclerosis in ten of the 11 patients. Left ventricular function was impaired when measured by end-diastolic pressure, end-diastolic volume, and ejection fraction. Segmental left ventricular contraction was severely abnormal. The abnormality of segmental contraction, distribution of coronary artery obstructions, an presence of collateral circulation were not different from other patients with severe occlusive coronary atherosclerosis. These 11 cases plus the 23 previously reported ante mortem form the total reported in world literature. The etiology of cornonary artery aneurysms is most commonly atherosclerosis (17/34, or 50 percent). The natural history of this condition is not known. Because of the severe atherosclerosis and poor distal-vessel run-off, most patients are not considered good surgical condidates; however, 15 patients have had coronary arterial surgery, and 13 have survived the immediate postoperative period with some improvement of symptoms.