Of the first 1,000 consecutive patients in our unit to receive aortocoronary bypass grafts, 108 have died: 32 at operation, 16 in hospital, and 60 late. Of 343 patients who had a normal ventricle, only 1 (0.29%) died at operation, and 2 of the 8 late deaths were noncardiac in cause. Most operative deaths resulted from low cardiac output, and most later deaths were caused by congestive heart failure. A study of the relation of various clinical and operative factors with mortality found that patients with congestive heart failure who underwent valve replacement and bypass grafting had the worst prognosis (73% mortality) while those undergoing bypass grafting with Class III or IV ventricular function (as we define it) and congestive heart failure were next (49% mortality).