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1. Panax ginseng is used to enhance stamina and relieve fatigue as well as physical stress. Ginsenoside, the effective component of ginseng, regulates cardiovascular function. This study was to examine the effect of ginsenosides Rb1 and Re on cardiac contractile function at the cellular level. Ventricular myocytes were isolated from adult rat hearts and were stimulated to contract at 0.5 Hz. Contractile properties analysed included: peak shortening (PS), time-to-90%PS (TPS), time-to-90% relengthening (TR90), and fluorescence intensity change (DeltaFFI). Nitric oxide synthase (NOS) activity was determined by the 3H-arginine to 3H-citrulline conversion assay. 2. Both Rb1 and Re exhibited dose-dependent (1-1000 nM) inhibition in PS and DeltaFFI, with maximal inhibitions between 20-25%. Concurrent application Rb1 and Re did not produce any additive inhibition on peak shortening amplitude (with a maximal inhibition of 24.9+/-6.1%), compared to Rb1 or Re alone. Pretreatment with the NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM) abolished the effect of Rb1 and Re. Both Rb1 and Re significantly (P0.05) stimulated NOS activity concentration-dependently. 3. This study demonstrated a direct depressant action of ginsenosides on cardiomyocyte contraction, which may be mediated in part through increased NO production.