Abstract: Objective: To study the influence of effective constituents of tribulus terrestris L on myocardial ischemic reperfusion injury(IRI).Methods: The extension of the myocardial areas,CK-MB activity and NO content in the serum,the content of ET-1 in the plasma,and the ultrastructure changes in myocardium were observed.Results: As compared with the sham-operated group,there were abnormal changes of myocardial ultrastructure in the model group,the level of NO in serum decreased,and the content of ET-1 in plasma increased after IRI.Effective constituents of tribulus terrestris L reversed the indices mentioned above markedly.Conclusions: This study shows that effective constituents of tribulus terrestris L may be regarded as an agent with a marked cardioprotective action against ischemia reperfusion induced myocardial injury by protecting the coronary endothelium in vivo model of the rat heart.