Abstract: Objective To determine the effect of tanshinone ⅡA on the transmembrance action potential of three layers of myocardial cells in LQT2 rabbit models. Methods Whole-cell patch clamp technique was used to record the action potential duration 90 (APD90) and the transmural dispersion of repolarization(TDR) of the epicardium, mid-myocardium and endocardium in the LQT2 rabbits. Results Of the three layers of myocardial cells, the mid-myocardium had the longest APD90 and the epicardium had the shortest APD90. The APD90 of all three layers of myocardial cells were shortened with infusion of 10 mg/mL tanshinone ⅡA. Their TDR values also reduced by the infusion. Conclusion Tanshinone ⅡA shortens APD90 and reduces TDR values.