Objective To study the effect of ranolazine combined ibutilide on rabbit with atrial fibrillation (AF) and their possible ionic mechanism of antiarrhythmic. Methods The rabbits were used to establish an acute AF model. They were randomly divided into two groups: combination group(n = 15) and ibutilide group(n = 15). The combination group received an intravenous bolus of 0. 1 mg·kg-1 ibutilide + 2 mg·kg-1 ranolazine,and ibutilide group only gave an intravenous bolus of 0. 1 mg·kg-1 ibutilide. Subsequently,both groups were maintained by intravenous infusion at a rate of 11 μg·kg-1·min-1. Twelve in each group,according to the electrocardiogram,the AF conversion time and the success rate of conversion after the two groups of administration,and the incidence of torsades de pointes tachycardia (Tdp) during the conversion were recorded. Three in each group, the whole cell patch clamp technique was used to record the myocardial cells of the two groups before administration (0 min). The rapid activation delay rectifier potassium current (IKr) change state and the action potential repolarization 90％ interval(APD90) at 30 min,60 min,120 min and 240 min after administration. Results The AF conversion rates in the combined group and the ibutilide group were 83. 33％ and 66. 67％; the AF conversion time in the two groups were (12. 13 ± 3. 15) ,(20. 16 ± 5. 42) min; the incidence of Tdp in the two groups were 0 and 8. 33％. Comparison between the combined group and the ibutilide group,the differences of the factors were significant (all P < 0. 05). Conclusion Ranolazine combined with ibutilide can significantly shorten AF conversion time,improve the success rate of transformation,and reduce the excitability of atrial myocytes.