This study examined whether exercise training of diabetic rats (streptozocin, 55 mg/kg) would affect the ability of perfused hearts to recover pump function after 75 min of ischemia and 30 min of reperfusion. All hearts were perfused with buffer containing the diabetic plasma concentrations of glucose and free fatty acids. Four groups were studied: sedentary control, trained control, sedentary diabetic, and trained diabetic. Trained control and diabetic rats were exercised on a treadmill at 5% grade, 21 m/min, 90 min/day, 6 days/wk for 8 wk. Sedentary diabetics had significantly lower body weight and elevated plasma glucose, triacylglycerol, and cholesterol relative to both control groups. Hearts from this group exhibited depressed postischemic recovery of pump function during reperfusion. In contrast, trained diabetic rats exhibited significantly lower plasma levels of triacylglycerol and cholesterol relative to sedentary diabetics. The postischemic recovery of cardiac pump function was improved in hearts from trained diabetic rats relative to sedentary diabetics. Exercise training had no effect on control rats. These results suggest that exercise training produces an antihyperlipidemic effect in diabetic rats and improves the tolerance of the diabetic heart to ischemia.