Comparison of 1085 patients having coronary bypass surgery without cardioplegia from Jan. 1970 to Aug. 8, 1977 with 1060 patients operated upon with cardioplegia from Aug. 9, 1977 to Dec. 31, 1980 suggests that improved myocardial protection afforded by cardioplegia combined with profound topical hypothermia has its principal impact in those patients requiring urgent or emergency operations by reducing the probability of intraoperative left ventricular failure after coronary bypass. The need for postoperative balloon pumping and the risk of intraoperative death were significantly lower in patients operated upon with hypothermia + cardioplegia myocardial protection. In patients who survived 30 days after operation there was no significant improvement in long-term survival, incidence of myocardial infarction, or recurrence of angina pectoris in the cardioplegia group despite a greater average number of grafts per patient and a smaller number of ungrafted but obstructed coronary arteries.