To investigate the effects of tertiary alkaloids and quaternary alkaloids of Rhizoma Corydalis on action potential and HERG channel, and to explore the mechanism of two alkaloids in anti-irrhythmia. Methods: Whole cell patch clamp technique was used to record the action potential of acutely isolated guinea pig ventricular myocytes and the HERG channel currents of cultured HEK293 cells stably transfected with HERG channel protein. Results: Tertiary alkaloids (30, 100 mg/L) could prolong APD90, and quaternary alkaloids (1, 3 mg/L) could shorten APD90 and enhance the resting potential. Quaternary alkaloids (30, 100 mg/L) prolonged APD90. Tertiary alkaloids (3-300 mg/L) inhibited HERG tail current amplitude in concentration-dependent manner. IC50 was 55 mg/L; quaternary alkaloids (1, 3 mg/L) could significantly increase HERG tail current amplitude, and quaternary alkaloids (30, 100 mg/L) could reduce the tail current amplitude. Conclusion:Corydalis tertiary alkaloids prolonged APD and inhibited HERG currents in concentration-dependent manner. Quaternary alkaloids in high concentration have the same effect as tertiary alkaloids and quaternary alkaloids in low concentration decrease APD and excite HERG currents, showing a double phase.