Abstract:Astragalus membranaceus saponins (AMS) 50~200μg/ml had a positive inotropic action on the isolated working heart of rats, but in the case of 30 μg/ml the inotropic action turned negative. The contractility recovered after washing out the AMS. Strophanthin K performed in a similar manner as AMS. AMS 500 μg/ml decreased the resting potential of cultured rat heart cells by 10 mV. The results suggest that AMS plays its inotropie role through influencing the Na-K-ATPase.