Abstract: AIM To investigate the effect of the phenolic alkaloids of menispermum dauricum (PAMD) on myocardial stunning in isolated rat heart. METHODS The chest of eighteen male Wistar rats were opened surgically and the hearts were rapidly excised and placed in an isovolumic isolated heart preparation vessel. After 15 min of stabilization, they were randomly divided into three experimental groups: myocardial stunning (S), control (C) and PAMD treated group (P). The hearts in the S group were subjected to a 10 min period of global ischemia followed by a 30 min period of reperfusion. The hearts in the P group were perfused with PAMD 0.5 mg·mL^-1 during a 10 min period of global ischemia followed by 30 min of reperfusion. The changes of the left ventricular systolic pressure (LVSP), the left ventricular end diastolic pressure(LVEDP) and ±dp/dt_max were monitored before ischemia and after reperfusion. The myocardial calcium contents were detected and the myocyte ultrastructural pathological alterations were observed. RESULTS At the end of reperfusion, the results of S group were: LVSP, +dp/dt_max and -dp/dt_max were decreased to 49% (P<0.001), 53% (P<0.01) and 58% (P<0.01) respectively, LVEDP were increased to 422% (P<0.01) of baseline compared with C group, the content of myocardial calcium was (514±142)μg·g^-1 dry weight (P<0.001 compared with C group (171±43)μg·g^-1 dry weight) and the reversible myocyte ultrastructural pathological injury was developed. On the other hand, 30 min after reperfusion, P group showed that the recovery of LVSP, LVEDP, +dp/dt_max and -dp/dt_max were improved to 70% (P<0.001), 205% (P<0.05), 78% (P<0.05) and 79% (P<0.01) respectively of baseline compared with S group, with (316±84) μg·g^-1 dry weight in myocardial calcium (P<0.01 compared with S group) and minor myocyte ultrastructural injury. CONCLUSION The results indicate that PAMD can attenuate the stunned myocardial dysfunction.