The ability to reverse acute coronary occlusion with fibrinolytic agents and percutaneous transluminal angioplasty has increased interest in the revascularization of ischemic myocardium. This study defines changes in global ventricular function, mass, and compliance during acute coronary occlusion and following reperfusion with blood in the beating and arrested heart. In 17 dogs on cardiopulmonary bypass, the proximal left anterior descending coronary artery was occluded for 45 minutes. In 12 dogs, flow was reestablished by releasing the coronary snare in the beating heart. In the other 5 dogs, the snare was released during a continuous 10-minute infusion of blood potassium cardioplegia in the arrested heart. Coronary occlusion resulted in significant decreases in stroke work index and left ventricular (LV) mass, but compliance was unchanged. Reperfusion in the beating heart increased LV mass compared with the values measured before ischemia (104 +/- 5 versus 95 +/- 5 gm; p less than 0.05) and decreased LV compliance (39 +/- 4 versus 53 +/- 4 ml at LV end-diastolic pressure of 8 mm Hg; p less than 0.05). In contrast, with blood cardioplegia-based reperfusion in the arrested heart, LV mass and LV compliance remained unchanged from control values. We conclude that revascularization of acutely ischemic myocardium in the beating heart further impairs LV function by increasing LV mass and decreasing compliance. This damage can be avoided by reperfusion with blood cardioplegia in the arrested heart.