AIM: To investigate the protective effect and mechanisms of di-ao-xin-xue-kang (DK) on myocardial ischemia-reperfusion. METHODS: Models of myocardial ischemia-reperfusion were constructed with sixteen mongrel dogs. The left ventricular pressure (LVSP), the marximal/minimum rate of LVSP (?dp/dt max) and the serum aspartate aminotransferase (AST), creatine kinase (CK), lactate dehydrogenase (LDH), malondialdehyde (MDA) were determined before and 90 minutes after occlusion, 120 and 240 minutes after reperfusion, and the MDA content in myocardial cell membrane prepared at 240 minutes after reperfusion was determined. The oxygen free radical was assayed with electron spin resonace spectroscopy (ESR) technique. RESULTS: ① LVSP and ?dp/dt max in the normal saline control (NS) group decreased with the time progress of occlusion-reperfusion, and it was the same in DK group, but the levels were significantly higher than that in NS group (P