Forty intracardiac-operative patients were divided into two groups randomly. Twenty patients were received by the improved St. Thomas Crystal Blood (1:4) Cardioplegia(Group A); 20 by the Shenmai liquid and improved St. Thomas Crystal Blood(1:4) Cardioplegia(Group B). During perioperation, the blood samples and myocardial tissue were collected, and clinical observations were recorded. The results showed that in Group B, contents of myocardial specific isoenzyme of creatine kinase(CK-MB), lactate dehydrogenase(LDH), malonyldialdehyde(MDA), and myocardial Ca2+ were significantly lower, the contents of superoxide dismutase(SOD) were, significantly better than that in Group A; and the histological findings showed less damage in Group B than in Group A. We conclude that Shenmai Cardioplegia can increase the myocardial protection of the intracardiac-operative patients. The possible mechanisms are that Shenmai liquids inhibit the production of oxygen free radicals and calcium paradox.