Objective:To study the effect of Xinjining extract(心悸宁,XJN) on inward rectifier potassium current(I_(K1)) in ventricular myocyte(VMC) of guinea pigs and its anti-arrhythmic mechanism on ion channel level. Methods:Single VMC was enzymatically isolated by zymolisis,and whole-cell patch clamp recording technique was used to record the I_(K1) in VMC irrigated with XJN of different concentrations(1.25,2.50,5.00 g/L;six samples for each).The stable current and conductance of the inward component of I_(K1) as well as the outward component of peak I_(K1) and conductance of it accordingly was recorded when the test voltage was set on -110 mV.Results:The suppressive rate of XJN on the inward component of I_(K1) was 9.54%±5.81%,34.82%±15.03%,and 59.52%±25.58%with a concentration of 1.25,2.50,and 5.00 g/L,respectively,and that for the outward component of peak I_(K1) was 23.94%±7.45%,52.98%±19.62%,and 71.42%±23.01%,respectively(all P<0.05).Moreover, different concentrations of XJN also showed effects for reducing I_(K1) conductance.Conclusion:XJN has inhibitory effect on I_(K1) in guinea pig’s VMC,and that of the same concentration shows stronger inhibition on outward component than on inward component,which may be one of the mechanisms of its anti-arrhythmic effect. Objective: To study the effect of Xinjining extract on inward rectifier potassium current (I_ (K1)) in ventricular myocyte (VMC) of guinea pigs and its anti-arrhythmic mechanism on ion channel level. Methods: Single VMC was enzymatically isolated by zymolisis, and whole-cell patch clamp recording technique was used to record the I_ (K1) in VMC irrigated with XJN of different concentrations (1.25, 2.50, 5.00 g / L; six samples for each) and conductance of the inward component of I_ (K1) as well as the outward component of peak I_ (K1) and conductance of it accordingly was recorded when the test voltage was set on -110 mV. Results: The suppressive rate of XJN on the inward component of I_ (K1) was 9.54% ± 5.81%, 34.82% ± 15.03%, and 59.52% ± 25.58% with a concentration of 1.25, 2.50, and 5.00 g / L, respectively, and that for the outward component of peak I_ (K1) was 23.94% ± 7.45%, 52.98% ± 19.62%, and 71.42% ± 23.01%, respectively (all P <0.05) .Moreover, different concentrations of XJN also showed effects for reducing I_ (K1) conductance.Conclusion: XJN has inhibitory effect on I_ (K1) in guinea pig’s VMC, and that of the same concentration shows stronger inhibition on outward component than on inward component, which may be one of the mechanisms of its anti-arrhythmic effect.