Sixty patients who had recurrent episodes of symptomatic atrial fibrillation or flutter, or both, and who had failed one to five prior drug trials were treated with open label oral propafenone hydrochloride. On a mean maximal tolerated dose of 795 +/- 180 mg/day, actuarial estimates of the percent of individuals free of recurrences of symptomatic atrial fibrillation/flutter during propafenone treatment were: 1 month, 54%; 3 months, 44% and 6 months, 40%. No individual baseline characteristic achieved statistical significance as a correlate of poor response to propafenone. Drug-related adverse reactions were reported in 22% of patients but were severe enough to require termination of propafenone in only 5%. Thus, oral propafenone is a useful and well tolerated drug for long-term suppression of symptomatic recurrences of atrial fibrillation/flutter despite a history of unresponsiveness to prior antiarrhythmic drug treatment.