Two hundred consecutive cases of aorta-coronary bypass operations were studied retrospectively to compare two methods of myocardial preservation. Patients with preoperative low cardiac output states, preoperative ventricular arrhythmias requiring treatment, and those who required concomitant additional procedures were excluded. Group I comprised the last 100 cases in which intermittent aortic cross-clamping and topical cardiac hypothermia were used for myocardial preservation. Group II comprised the following first 100 cases in which cold hyperkalemic solution (modified Roe’s solution) was injected into the aortic root for myocardial preservation. Mean total aortic cross-clamp times were 40 minutes in Group I and 44 minutes in Group II. Mean perfusion times were 2 hours 21 minutes in Group I and 1 hour 56 minutes in Group II (p < 0.01). This difference is due to the longer period of reperfusion required in Group I. In the postoperative period, electrocardiographic evidence of perioperative myocardial infarction developed in 8 percent of Group I as opposed to 2 percent in Group II (p = 0.02). Arrhythmias requiring treatment were seen in 28 percent of Group I and 8 percent of Group II patients (p < 0.001). Mean CPK II was 54 I.U. in Group I and 22 I.U. in Group II (p < 0.0001). CPK II elevation over 100 I.U., thought to be indicative of myocardial infarction, was seen in 15 percent of Group I and 3 percent in Group II (p < 0.01). There were two hospital deaths in Group I and one hospital death in Group II. These results indicate that protecting the myocardium with cold hyperkalemic arrest (with modified Roe’s solution) is superior to use of intermittent cross-clamping, and topical cardiac hypothermia for aorta-coronary bypass surgery.