Total occlusion of the left main coronary artery (LMT) is rarely demonstrated with coronary angiography. All patients with LMT occlusion are of necessity dependent upon collateral circulation from the right coronary artery, which in approximately two thirds of patients is jeopardized because of marked obstruction of the right coronary artery. The ultimate example of collateral flow is provided by the following case. A 64-year-old man, who had total proximal left main and right-coronary artery occlusion, underwent coronary artery bypass grafting. On coronary angiogram, his jeopardized collateral artery was conus branch and only the LAD was graftable for coronary artery bypass surgery. One saphenous vein graft was bypassed to the LAD. Postoperatively, the left ventricular function improved considerably and the ejection fraction of the left ventricle rose to 46% from 23% preoperatively.