Data on short and long term efficacy and safety of d,l sotalol in patients with atrial fibrillation or atrial flutter is limited. The aims of this study were to (1) assess the antiarrhythmic efficacy of d,l sotalol maintaining normal sinus rhythm in patients with refractory atrial fibrillation or flutter, (2) evaluate the efficacy of d,l sotalol in preventing recurrences of paroxysmal atrial fibrillation or flutter, (3) evaluate the control of ventricular rate in patients with paroxysmal or refractory atrial fibrillation or flutter unsuccessfully treated with other antiarrhythmic agents, (4) determine predictors of efficacy (5) assess the safety of d,l sotalol in this setting. Two hundred patients with chronic or paroxysmal atrial fibrillation or atrial flutter or both, who had failed one to six previous antiarrhythmic drug trials were treated with d,l sotalol 80 to 440 mg/day orally. Fifty four percent was female, age 47 +/- 16 years (range 7-79), follow up period 7 +/- 7 months (range 1 to 14 months), 79% of patients had the arrhythmia for more than one year. The atrial fibrillation in 37.5% of patients was chronic and paroxysmal in 23.5. The atrial flutter was chronic in 31% of patients and paroxysmal in 8%. Eighty two percent of patients was in functional class I (NYHA) and 82% had cardiac heart disease: left atrial (LA) size 44 +/- 10 mm, right atrial (RA) size 37 +/- 7 mm and left ventricular ejection fraction (LVEF) 58 +/- 8%. Total success was achieved in 58% of patients (atrial fibrillation 40% and 18% in atrial flutter), partial success in 38% (atrial fibrillation in 18% and 20% in atrial flutter) and 4% of patients failure. It was p < 0.07 when compared total success vs partial success among atrial fibrillation and atrial flutter groups. Patients with cardiac heart disease responded worst (p = 0.10) to the drug than those without it, specially if the heart was dilated. We concluded that d,l sotalol has moderate efficacy to convert and maintain normal sinus rhythm, as well as it acts controlling paroxysmal relapses and ventricular heart rate.