Abstract: AIM: Investigate the changes of Na+ current characteristics and SCN5A expression in the human chronic atrial fibrillation (AF). METHODS: Na+ currents were recorded with the whole-cell patch clamp technique in single atrial myocyte of AF group and normal sinus rhythm group (SR group)．The sodium channel α-subunit gene (SCN5A) mRNA was measured by reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: (1) neither current density nor time-dependent recovery of INa was altered by AF in human, but voltage-dependent inactivation of INa was shifted to more positive voltages in AF cells. (2) AF didn't affect mRNA concentration of SCN5A. CONCLUSION: INa is not the reason for the decrease of atrial conduction velocity in AF.