The value of reversion of chronic, established atrial fibrillation has been assessed by reviewing the status of 50 patients after at least 3 months and after an average of 11 months following attempted reversion. Only 19 of these patients maintained normal rhythm, a proportion which is similar to most previously reported experiences by others. At least one instance of ventricular fibrillation due to quinidine sulfate occurred. Within this relatively small group, normal rhythm was successfully maintained almost exclusively in patients with hemodynamically minor heart disease or in those who had undergone ameliorative cardiac surgery. Although the simplicity and immediate efficacy of the reversion procedure was again demonstrated, its value in patients whose chronic atrial fibrillation was associated with stable or progressive congestive heart failure appeared to be limited.