Abstract: Aim ：To study the effects of berberine(Ber) on the rapidly activating component(I _Kr )，the slowly activating component(I _Ks) of the delayed rectifier potassium current and the inward rectifier potassium current(I _K1) in cardiomyopathic guinea pig ventricular myocytes. Methods ：After guinea pigs were ip L-thyroxine 0.5 mg/kg for 10 d，their hearts were cardiomyopathic.Then whole cell patch-clamp recording technique was used to observe the effect of 30 μmol/L Ber on the I _Kr ，I _Ks and I _K1in cardiomyopathic guinea pig ventricular myocytes. Results ：In cardiomyopathic guinea pig ventricular myocytes，Ber 30 μmol/L markedly inhibited I _Kr and I _Ks by 22.8% and 29.5% at +10 mV and +80 mV，respectively.The effect of Ber on I _Ks was greater than that on I _Kr .Ber 30 μmol/L also inhibited the inward component of I _K1 by 29.1% at+120 mV，but the reverse potential of I _K1was unaffected.Ber(1- 300 μmol/L) was shown to inhibit I _Kr and I _Ks in a concentration-dependent manner.Their IC₅₀ were 76.74 μmol/L and 55.37 μmol/L，respectively. Conclusion ：Ber inhibited I _Kr ，I _Ks and I _K1in cardiomyopathic guinea pig ventricular myocytes，which may be important in understanding the antiarrhythmic effects of this drug.