AIM AstragalosideⅣ (AS-Ⅳ) is one of the main active constituents of astragalus membranaceus, the present study is to investigate the effects of AS-Ⅳ on action potentials and membrane currents.METHODS The electrophysiologic effects of AS-Ⅳ were checked in freshly isolated guinea pig ventricular myocytes with whole-cell patch clamp technique.RESULTS AS-Ⅳ 1 × 10-6 tool.L-1 significantly prolonged the action potential duration at 95% repolarization (APDg5) from (313.1-+ 38.9)ms to (785.3 ±83.7) ms.AS-Ⅳ at 1 × 10-6 mol· L-1 enhanced the inward rectified potassium currents (IK1) and inhibited the delayed rectified potassium currents (IK).AS-Ⅳ at 1 × 10-6 mol·L-1 depressed Ca2+ current (Ica) from (-607.3 ± 37.5)pA to (-321.1 ±38.3)pA.AS-Ⅵ increased the intracellular Ca2+ release by 3 times.CONCLUSION AS-Ⅳ prolonged APD of guinea pig ventricular myocytes, and might handle Ca2 + signaling through suppression of ICa and strengthening the intraeellular Ca2 + release.