Potassium-induced cardioplegia during anoxic arrest was utilized in a study of 190 consecutive patients undergoing revascularization (average 2.8 grafts per patient) from August, 1975, through August, 1976. Surgical technique, moderate systemic hypothermia with intermittent anoxic arrest, and the surgeon were the same for all patients. One hundred thirty-five patients (KC1-treated) received a bolus (150 ml.) of potassium solution injected into the proximal aortic root whenever the aortic cross-clamp was applied; 55 others served as control subjects. The mortality rate was 2.2% (three of 135) in the KCl-treated group and one of 55 in the control group. New Q waves appeared in 5.9% (eight of 135) of the KCl-treated patients and 11% (6 of 55) of control subjects (p = N.S.). Catecholamine drips were required after bypass in 4.4% (six of 135) of patients given potassium and 18% (10 of 55) of control patients (p less than 0.05). Profound myocardial relaxation was of added technical value with potassium. It is our impression that hearts treated with potassium exhibited more prompt cardioversion, separated from cardiopulmonary bypass with less need for inotropic support, and exhibited less myocardial injury during the revascularization procedure.