Among 60 patients randomly assigned to a reperfusion pressure of 50 mm Hg or one of 75 mm Hg (30 mm Hg during the first 2 minutes in both groups) during initially hyperkalemic, controlled aortic root reperfusion after coronary artery bypass grafting, no in-hospital deaths occurred, no patient received an intraaortic balloon pump, no patient had new Q waves, and creatine kinase MB release was similar in the two groups. Median interval between the beginning of reperfusion and the return of rhythmic cardiac contractions in the 50 mm Hg group was 7 minutes; in the 75 mm Hg group, it was 5 minutes (P = 0.1). The initial reactive hyperemic response was greater in the 75 mm Hg group. There were no believable differences (P < 0.1) between the two groups in postoperative cardiac output, left and right atrial pressure, arterial blood pressure, and prevalence of catecholamine administration.