The effects of lipoic acid on intensity of free radical reactions, citrate content, and aconitate hydratase during myocardial ischemia have been investigated. Treatment with lipoic acid normalized biochemiluminescence parameters and citrate level, which were increased in the myocardial pathology. Treatment with lipoic acid also increased specific activity of aconitate hydratase, which was decreased in myocardium and blood of animals with myocardial ischemia. Administration of lipoic acid decreased DNA fragmentation observed during myocardial ischemia. The data suggest that lipoic acid can be effectively used as a cardioprotector preventing the development of free radical oxidation during myocardial ischemia.