This study introduces the immunosuppressor, cyclosporin A, as a cardioprotective drug. This effect was analyzed during development of reperfusion/induced arrhythmias after 5-min period of coronary ligation in hearts of rats under anesthesia. The results indicate that cyclosporin, when given before coronary occlusion, at a dose of 20 mg/kg, effectively protects against the high incidence of arrhythmias and the fall in blood pressure induced by reperfusion. In addition, it inhibits the delivery of lactic dehydrogenase and creatine kinase enzymes to the plasma. We propose that the protective effect could be related with its well documented action to restrain Ca2+-induced damage of mitochondrial functions.