OBJECTIVE To investigate the effect of oxymatrine(OMT) on tumor necrosis factors(TNF) and malondialdehyde(MDA) during myocardial ischemic reperfusion injury in rats and its protective mechanism.METHODS Male Wistar rats were anesthetized,and the left coronary artery was ligated for 30 min and reperfused for 180 min.Sixty four male Wistar rats were divided into four groups randomly(n=16):①sham operated group;②myocardial ischemic reperfusion injury group(MIR);③60 mg·kg^-1 treated group;④120 mg·kg^-1 treated group.Rats were given oxymatrine intraperitoneally 5 min before acute ischemia and the infusion time last 5 min.TNF and MDA were measured before the occlusion of the coronary artery,30 min after ischemia and 90,180 min after reperfusion.TNF was detected by immunohistochemistry.MDA was determined by thiobarbituric acid(TBA).At 180 min after reperfusion,myocardial ischemic specimens were taken to study ultrastructure by using electron microscopy.RESULTS ①The expression of TNF was increased after reperfusion.The TNF express of OMT treated groups decreased significantly compared with MIR group after 180 min reperfusion.There was no difference in the expression of TNF between both treated groups.②A significant elevation of MDA was observed after reperfusion. Compared with MIR group,the content of MDA in OMT groups was markedly decreased(P<0.05) after 180 min reperfusion.There was no significant difference in the level of MDA between two treated groups.③Electron microscopic examination showed the pathological changes of OMT groups were ameliorated.CONCLUSION Oxymatrine protects heart from ischemic reperfusion injury in experimental ischemia reperfusion rats.And this effect is showed without a dose dependent manner.