To investigate the effects of Zhigancao Decoction on L-type calcium current(ICa-L) and the kinetics characteristics of atrial myocytes in rats.Methods:Twenty-four rats were randomly divided into a control group and low-dose(1.125 g/mL)，medium-dose(2.25 g/mL)，and high-dose(4.5 g/mL) Zhigancao Decoction groups，with six rats in each group.The rats in the Zhigancao Decoction groups were treated correspondingly by gavage，and those in the control group received an equal volume of normal saline.One week after the administration，atrial myocytes in the four groups were acutely isolated by enzymatic hydrolysis.The ICa-L of atrial myocytes in the four groups was recorded by the whole-cell patch clamp technique and the I-V curves were compared.The kinetics characteristics of ICa-L channels of atrial myocytes were compared between the medium-dose Zhigancao Decoction group and the control group.Results:Compared with the control group，the Zhigancao Decoction groups showed inhibited ICa-L of atrial myocytes and upward-shifted I-V curves.As revealed by the comparison of kinetics characteristics of ICa-L channels between the medium-dose Zhigancao Decoction group and the control group，the differences in the activation curve and half activation voltage of cells between the two groups were not significant(P>0.05)，but in the middle-dose Zhigancao Decoction group，the homeostatic inactivation curve shifted to the right，and the half-deactivation voltage V1/2 was increased(P<0.05).Additionally，the curve of recovery after inactivation shifted downward，and the time constant(τ) was prolonged(P<0.01).Conclusion:Zhigancao Decoction can inhibit the ICa-L of atrial myocytes in rats，delay the inactivation speed of calcium channels in atrial myocytes，and prolong the recovery time after inactivation，thereby achieving the effect of slowing down the heart rate.It may be the mechanism of Zhigancao Decoction in the clinical treatment of atrial arrhythmia.