Abstract: AIM To study the tonic block and use-dependent block of transient sodium current (INa-T) by propafenone in rabbit ventricular myocytes. METHODS INa-T was measured and I-V curves of INa-T obtained using whole cell patch clamp before and after the perfusion of propafenone (10 μmol/L). RESULTS After the perfusion of propafenone, the I-V curve of INa-T shifted upward and the peak current decreased ［(3001±383) pA vs.(4193±378) pA, P<0.05］. After perfusion of propafenone, when stimulated at 0.06 Hz and 1 Hz, no significant use-dependent block was observed, whereas with stimulation at 2, 5 and 10 Hz, significant use-dependent block of INa-T was found with inhibition fractions of (22±11)%, (38±14)% and (52±17)%, respectively, with statistically significant difference when compared between any two of the three groups and compared with the inhibition fractions at 0.06 Hz and 1 Hz (P<0.05). CONCLUSION Propafenone produces significant tonic block and use-dependent block of INa-T.