Open chest dogs undergoing 30-min occlusion of the left anterior descending coronary artery (LAD), followed by 20-min reperfusion, received silibinin (2 mg/kg body weight), allopurinol (100 mg for two days as pretreatment, 20 mg/kg body weight during ischemia and reperfusion), superoxide dismutase (SOD, 5 and 0.5 mg/kg body weight, starting from the last minute of ischemia over 6 min). Control and treated dogs were comparable with respect to myocardial regional contractile force (strain gauge), malondialdehyde (MDA) and creatinine kinase (CK) levels of sinus coronarius blood samples, heart rate, and blood pressure. Allopurinol and large doses of SOD produced significant improvement in contractility and decreased MDA levels, which might suggest free radical mediated reactions during reperfusion.