Oxidant stress has a role in pathophysiology of many diseases. How¬ever its role in myocardial infarction is not frilly clear. Atso,prostaglandins have a relation to many diseases hover ,its relation to myocardial infarc¬tion is not fully investigated Also it is not known well whether prosta¬glandins mediate the cardioprotective effect of anti-oxidant vitamins E and C. The aim of the present work was to investigate the role of oxidant stress and prostaglandin in the pathgenseis of myocardial infarction and possible relation between them The results of the present study showed that injection of vitamin E and vitamin C ( Known anti-oxidant vitamins) reduced the myocardial infarction induced by isoprenalin injection .thus denoting that the myocardial infarction is largely due to oxidant stress . Also the results showed that injection of voltaren (a prostaglandin syn¬thesis inhibitor) caused an increase in myocardial infarction induced by isoprenalin sign fying a prostaglandin cardioprotective action. The results showed also that injection of voltaren together with vitamin E nearly abol¬ished the cardioprotective action of vitamin E. This .proved that the card i -` oprotective effect of vitamin is mediated at least partially through prosta¬glandin . In contrast ,tr4ection of voltaren with vitamin C did not affect the cardiprotective action of vitamin C.This means that the cardiprotective ac¬tion of vitamin C is not mediated through prostaglandin.