Abstract: AIM: To investigate the mechanism of antiarrhythmic action of benzylenzyl-tetrahydropalmatine(BTHP). METHODS: The effects of BTHP on potassium currents, calcium and sodium currents were studied in guinea pig single ventricular myocytes by using whole cell patch clamp technique. RESULTS: BTHP was shown to effectively block the two components of delayed rectifier potassium(I_K), ie I_Kr and I_Ks. I_Kr and I_Kr,tail were reduced from (0.68±0.27)　pA/pF and (0.94±0.44)　pA/pF to (0.47±0.18)　pA/pF and (0.60±0.32)　pA/pF, respectively by BTHP (30　μmol.L^-1) in a frequency-dependent fashion. I_Ks and I_Ks,tail were obviously inhibited from (12.1±1.78) pA/pF and (4.22±0.56) pA/pF to (7.25±0.87) pA/pF and (2.58±0.91) pA/pF after exposure to 30 μmol.L^-1 BTHP. I_Ca，L was also decreased from (14.48±0.26)　pA/pF to (10.44±0.32)　pA/pF by BTHP（200　μmol.L^-1）,　but BTHP was shown not to affect IK1, I_Ca,T and I_Na. CONCLUSION: BTHP significantly blocked I_Kr，　I_Ks and I_Ca，L, while I_Kr was inhibited by BTHP in a frequency-dependent fashion.