A 28-year-old woman underwent cardiac catheterization three months after sustaining an acute anterolateral myocardial infarct. An aneurysm of the left main coronary artery was found at angiography and also was visualized by two-dimensional echocardiography. The patient had no evidence of atherosclerotic vascular disease. At operation, vein grafts were placed to bypass the aneurysm and the orifice of the left coronary artery was oversewn to exclude the aneurysm from the coronary circulation. © 1979, The Society of Thoracic Surgeons. All rights reserved.