Objective To investigate the protective effect of Shenfu injectio (SFI) pretreatment on myocardium in patients undergoing cardiac valve replacement with cardiopulmonary bypass (CPB). Methods Thirty ASA Ⅱ or Ⅲ patients with cardiac function Ⅱ or Ⅲ, aged 18-51 yr, weighing 45-73 kg, scheduled for elective cardiac valve replacement under CPB, were randomly divided into 2 groups (n = 15 each): control group and SFI group. In SFI group, shenfu injectio 1.5 ml/kg (dissolved in 5% glucose or normal saline) was infused iv once a day for 5 days before operation and then infused again for 30 min before anesthesia induction. In control group, shenfu injectio was not given and the other procedures were the same as those in SFI group. Venous blood samples were drawn immediately before aortic clamping (T_1), and at 10 min (T_2), 30 min (T_3), 2 h (T_4), 24 h (T_5) and 48 h (T_6) after aortic unclamping for determination of plasma CK-MB and LDH activities. Blood samples were taken from coronary sinus at T_(1-3) for determination of plasma MDA and cardiac troponin I (cTnI) concentrations, and SOD activity. Myocardial tissues of right ventricle were taken at T_1 and immediately after aortic unclamping to observe the myocardial ultrastructure (using electron microscope). The rate of spontaneous heart beat, consumption of vasoactive drugs, and aortic clamping time were recorded. Results Plasma cTnI and MDA concentrations at T_(2,3), and CK-MB and LDH activities at T_(2-6) were significantly increased and SOD activity at T_(2,3) was significantly decreased compared with those at T_1 in two groups (P < 0.05 or 0.01). Plasma cTnl and MDA concentrations at T_(2,3), and CK-MB and LDH activities at T_(2-6) and consumption of dopamine and nitroglycerin were significantly lower and SOD activity at T_(2,3) and rate of spontaneous heart beat significantly higher in SFI group than in control group (P < 0.05 or 0.01). Microscopic examination showed that the injury to mitochondrial ultrastructure was attenuated in SFI group compared with control group. Conclusion Shenfu injectio can protect myocardium in patients undergoing cardiac valve replacement with CPB to some extent and the mechanism may be related to inhibition of lipid peroxidation. Key words: SHENFU DECOCTION; Myocardial reperfusion injury; Extracorporeal circulations; Heart valve prosthesis implantation