For the primary analysis, AF burden will begin to be tabulated after an initial run in period for each study drug. For patients starting sotalol, the run-in period will coincide with the first 5 doses (60 hours). For patients starting flecainide, the run-in period will last until a dose of at least 200 mg per day (in divided doses) is achieved, unless a smaller dose is the maximally tolerated dose. Ideally, this will be achieved within 3-4 days after initiation of flecainide. If, during the course of the study, a patient develops persistent AF, a cardioversion will be scheduled in coordination with the patient's primary cardiologist or electrophysiologist. The patient will then be switched to the other study drug. In case of such an occurrence, AF burden will be tabulated using an "on treatment" analysis. Conditions for which a patient will be withdrawn from the study and data censored will be discontinuation of AAD therapy, initiation of amiodarone, AF ablation or AV node ablation/permanent pacing, loss to follow-up, elective withdrawal from the study, or death.