Abstract: OBJECTIVE To study the effect of Ziziphora clinopodioides flavonoids(ZCF) on myocardial ischemia reperfusion(I/R) injury in isolated rat hearts. METHODS Fourteen Sprague-Dawley rats were randomly divided into five groups: normal control group, I/R group and ZCF group(12.5 mg?L^-1，25 mg?L^-1，50 mg?L^-1). Langendorff-perfusion isolated rat hearts were prepared. During myocardial ischemia reperfusion, the left cardiac function was measured by the analysis system, such as +dp/dt_max, -dp/dt_max, LVEDP, CF and HR. The activities of creatine kinase(CK), lactate dehydrogenase(LDH) in myocardial tissues were measured to evaluate the injury of myocardial cells and the protective effect of ZCF. Meanwhile, the activity of superoxide dismutase(SOD) and the contents of malondialdehyde(MDA) in myocardial tissues were determined. RESULTS Compared with the I/R group, ZCF 25 and 50 mg?L^-1 could recover cardiac function, and reduce the release of CK, LDH from I/R rat hearts. It could increase the activity of SOD, and decrease the MDA product(P<0.001, P<0.01 or P<0.05). CONCLUSION ZCF possesses protective effect on isolated heart I/R injury. The mechanism may include the remaining of myocardial enzymes activity(CK, LDH ) in cardiac muscle except scavenging oxygen free radical, reducing lipid peroxidation.