Systemic hypothermia at 25 degrees-28 degrees C without chemical cardioplegia was used in 908 patients undergoing coronary artery bypass grafting. Local coronary artery flow was interrupted only during grafting of a distal anastomosis. Systemic perfusion pressure was maintained at 80-100 mmHg, hematocrit at 20%-25%, and pCO2 and pH were monitored during hypothermia according to the alpha-stat principle, while the left ventricle was vented routinely. Proximal anastomoses were performed just before extracorporeal circulation was started by only partially occluding the ascending aorta. Preoperatively 61.9% of the patients had had a myocardial infarction, and 44% had unstable angina. In 14% a severe lesion of the main stem of the left coronary artery was present. Left ventricular function was moderately depressed in 25% and severely depressed in 8% of the patients. Forty-eight patients (5.3%) were aged 70 years or older. The mean number of grafts placed per patient was 3.3. Perioperative myocardial infarction occurred in 3%. Death due to left ventricular failure occurred in 0.4%. No left ventricular assist devices were needed; an intra-aortic balloon pump was used in 1%; positive inotropic support was required in 3.8% of the patients. These results indicate that systemic hypothermia alone provides safe myocardial protection and in certain cases may be the method of choice, particularly if aortic cross clamping or administration of cardioplegic solution is contraindicated. In addition, this method provides rapid revascularization of a severely ischemic zone, as present after unsuccessful PTCA procedures.