Free- radicals are generated in the minutes following myocardial re-perfusion and this could be the cause of myocardial injury during by Pass surgery. Pretreatment with antioxidants could effectively attenuate re-perfusion injury during global ischemia.Xanthine dehydrogenase is converted into xanthine oxidase and this causes accumulation of hypoxanthine and xanthine in the cell. When re-perfusion starts, fresh oxygen interacts with xanthine oxidane and hypoxanthine to form superoxide anion radical O2.- . Allopurinol can metabolically block the formation of reduced oxygen radical by inhibiting...