Objective:To investigate the effect of Cyclovirobuxine D（CVB-D） on action potentials in isolated guinea pig ventricular myocytes.Methods:The single myocytes were enzymatically obtained from the guinea pig hearts and the action potentials were examined by whole-cell patchclamp technique.Results:4×10

-4

g/L CVB-D decreased action potential amptitude（APA）from 113.3±6.3 mV to 110.2±6.4 mV（n=6

P

<

0.01）

prolonged action potential duration of repolarization 50%(APD

50

)from 616.3±68.0 ms to 657.4±79.5 ms（n=6

P

<

0.01）

prolonged action potential duration of repolarization 90%(APD

90

)from 633.5±71.2 ms to 669.2±74.4 ms（n=6

P

<

0.01）

Prolonged action potential duration of repolarization 50% to repolarization 90%(APD

50-90

)from 15.9±6.0 ms to 20.1±5.2 ms（n=6

P

<

0.01）

and decreased decay slope of phase 3（V

3

） from-2.6±0.8 V/s to-2.4±0.7 V/s（n=6

P

<

0.01）.Compared with the baseline

4×10

-3

g/L CVB-D makes the APD

50-90

pass to increase trend gradually

but the variety trend of the V

3

decrease gradually

other index sign varieties are consistent.Conclusion:CVB-D decreased APA and V

3

and prolonged APD

50

APD

90

APD

50-90

which may be its mechanism of positive inotropic effect and antiarrhythmic effect.