Background and Objectives: Pretreatment of antiarrhythmic drugs are suggested to facilitate electrical cardioversion (CV) of chronic atrial fibrillation (AF). We assessed the efficacy of acute intravenous amiodarone as pretreatment before repeating CV in chronic AF patients in whom direct current (DC) CV has failed to convert AF to sinus rhythm (SR). Methods: Of 71 chronic AF who underwent DC CV for 1 year at our institute, SR was restored in 49 patients (initial success rate: 69%) and failed in 22 patients. 16 of 22 patients in whom DC CV failed were included (M:F= 13:3, mean age=60짹3yrs, mean duration of AF = 30짹5 month) in this study. After unsuccessful transthoracic CV with step-up protocol in which shocks at 70J, 100J, 150J with biphasic waveform of cardioverter, amiodarone (150mg, 300mg) was infused over 10 minutes and transthoracic CV reattempted. Results: SR was restored with repeated CV after amiodarone infusion in 7 of 16 patients who were resistant to initial attempt of CV (Success rate after amiodarone infusion = 44%, Group 1; successful, Group 2; unsuccessful). Baseline clinical and echocardiographic findings were similar between two groups except that the ejection fraction (EF) was lower in Group 1 than in Group 2 (45짹3% vs 54짹2%, p<0.05). In successful group, mean cumulative dose of electrical shock to convert SR prior to amiodarone infusion was 225짹12J and that after amiodarone infusion was 207짹12J (p=ns). 3 of 7 patients in whom CV was successful after amiodarone infusion and then maintained low dose of oral amiodarone recurred AF within one month (short term AF recurrence rate=43%, mean duration=14 days). Conclusion: In chronic AF patients in whom first DC CV has failed, pretreatment with intravenous loading of amiodarone before repeated CV increased success rate to restore SR. However, SR maintenance was not lasted longer than one month in 43% of the successfully cardioverted group after amiodarone infusion.