Abstract: Standard microelectrode technique and the whole-cell clamp technique were used to investigate the effects of tetrandrine and rotundine on the action potential of rabbit sinus node dominant pacemaker cell and calcium currents of ventricular myocytes from guinea pig. The results indicate that: tetrandrine 1～200 μmol·L^-1 and rotundine 3～300 μmol·L ^-1 decreased the action potential amplitude(APA), the maximal upstroke velocity (Vmax), spontaneous depolarizing velocity of phase 4(SP₄) and prolonged the sinus circle length(SCL) in a dose dependent manner. Tetrandrine 0.1 μmol·L^-1 in combination with rotundine 0.3 μmol·L^-1 was shown to effectively reduce the I_Ca of ventricular myotytes from guinea-pig, the rate of inhibition is 19.6%. The results suggest that the two drugs have a good synergistic effect on inhibiting calcium current. These results might also put forword a valueable theoretic base for using the two drugs together in treating patients.