AIM:To investigate the effect of batroxobin on thromboxane A 2(TXA 2)level in canine heart ischemia/reperfusion (I/R) injury and the cardioprotective mechanism of batroxobin against I/R injury. METHODS: Canine heart ischemia was induced by ligation of the left anterior descending coronary artery for 30 min followed by 90 min reperfusion.Batroxobin was intravenously administered before heart ischemia and 15 min before reperfusion.The level of plasma thromboxane (TXA 2) ,creatine phosphokinase (CK), lactic dehydrogenase (LDH ) and the concentration of myocardial TXA 2 were measured. The pathological changes in I/R myocardium were observed. RESULTS: In I/R group, TXA 2 levels of both plasma and myocardium increased significantly,and myocardium was injured obviously. Myocyte cells of central zone of I/R heart showed intracellular edema, swollen and damaged mitochondria, and fragmentation of cristae and concentrated nucleus. Plasma CK and LDH level was also elevated. Both ways of batroxobin administration reduced TXA 2 level apparently and plasma CK?LDH were also reduced significantly. LVEDP lowered while +dp/dt max elevated greatly,the mortality of I/R canine reduced obviously. CONCLUSION: Batroxobin decreased TXA 2 levels of both plasma and myocardium significantly, and could afford protection from I/R injury.