Abstract: Flow-through to increase the duration of action potential at 20 and 90% of repolarization of isolated guinea pig papillary muscles. However, the amplitude of action potential, the resting potential and the overshoot, and maximum rate of 0 phase depolarization (Ⅴ_max) remained unchanged.The membrane potential was held at 40 mV and command potential at-15mV, 0.3 Hz 500 ms. After,10 min of perfusion of EBP 30 μmol/L, the slow inward current (Ⅰ_Si)was reduced markedly. When the holding potential Was held at-20 mV., and the command potential at+10 mV, EBP (10～100μmol/L)exerted a depressed effect on the delayed (outward) rectifier current (Ⅰ_X) in a dose-dependent manner.It may be concluded that the antiarrhythmic effects of EBP is mainly related to decrease the automaticity and prolong the duration of action potential at 20～90% of repolarization of isolated guinea pig papillary muscles.