Objective:To investigate effects on action potential(AP) of Spraque-Dawley rat by different isomers of amlodipine(Aml). Methods:Calcium-tolerant ventricular myocytes were isolated by enzyme digestion. AP changes in S-Aml,R-Aml and R,S-Aml with concentrations of 0.1,0.5,1.0,5.0 and 10.0 μmol/L were recorded respectively by whole cell configuration patch clamp. Results:①AP maximal velocity,AP amplitude and overshoot had no significant changes in S-Aml,R-Aml and R,S-Aml with concentrations of 0.1,0.5,1.0,5.0 and 10.0 μmol/L(P > 0.05); ②Fifty percent of Action potential duration(APD50) were(36.2 ± 8.2)-(33.9 ± 7.7)-(30.2 ± 6.8)-(22.6 ± 5.1) and (15.1 ± 3.4)ms,respectively(P < 0.05) with the increase of S-Aml concentrations from 0.1 μmol/L to 10 μmol/L;APD50 were (39.2 ± 9.2),(36.7 ± 7.9),(33.8 ± 7.2),(25.4 ± 5.9) and (21.7 ± 5.2)ms,respectively(P < 0.05) with the increase of P,S-Aml concentrations from 0.1 μmol/L to 10 μmol/L;APD50 were(45.1 ± 11.3),(46.2 ± 10.8),(44.9 ± 7.3),(44.8 ± 8.2) and (45.7 ± 9.4)ms,respectively(P > 0.05) with the increase of P-Aml concentrations from 0.1 μmol/L to 10 μmol/L. Conclusion:APDs were gradually shortened with the increase of S-Aml and R,S-Aml concentrations. S-Aml and R,S-Aml might influence APDs by blocking L-type calcium channel;R-Aml had no effect on APD,and might have no influence on L-type calcium channel.