BACKGROUND AND OBJECTIVES: Various intravenous (IV) antiarrhythmic drugs in patients with atrial fibrillation (AF) refractory to electrical cardiooversion have been attempted. We assessed the efficacy of IV propafenone in patients with AF who failed to achieve normal sinus rhythm using standard external direct current (DC) cardioversion. SUBJECTS AND METHODS: Of the 77 AF patients who underwent a DC cardioversion, 18, who were refractory for up to a maximal 360 joules of external DC cardioversion, were included in this study. Propafenone was infused for 10 minutes at doses of 2 mg/kg (n=3), 2.5 mg/kg (n=8), and 3 mg/kg (n=7) followed by repeated DC cardioversion. RESULTS: The mean age of the patients receiving propafenone was 55+/-14 years and 21% were women. The mean ejection fraction and the average diameter of the left atrium were 56+/-5% and 42+/-7 mm, respectively. The AF cycle length increased following propafenone infusion form 160+/-23 ms to 278+/-62 ms (p<0.05). The AF converted to a normal sinus rhythm following propafenone infusion in three patients. Thirteen patients were successfully cardioverted following IV propafenone infusion, with a mean accumulated energy of 410+/-216 joules (689+/-373 joules prior to propafenone infusion, p<0.05). Cardioversion failed in 2 patients;therefore, the success rate of the cardioversion in patients who received IV propafenone was 88.9% (16/18). No significant adverse effects were observed. CONCLUSION: IV propafenone can be safely used to enhance the efficacy of cardioversion in patients with AF refractory to transthoracic DC cardioversion.