Acute termination of AF is almost always successful by external electrical cardioversion, especially using recently optimized techniques [biphasic shock wave forms, anterior-posterior electrode position, sintered steel electrode paddles. Maintaining sinus rhythm, however, is a more difficult task. Antiarrhythmic, ion channel-blocking drugs are effective in preventing a part of recurrent episodes of AF. Their long-term use, however, is limited by pro-arrhythmic side effects which are especially apparent during long-term therapy. AF initiates major changes in atrial electrophysiology per se which have been summarized as "electrical remodeling". The main consequence of these changes is a shortening of the atrial refractory period and action potential duration. Electrical remodeling maintains AF and is related to recurrence of AF after successful cardioversion. Electrical remodeling is reversed when sinus rhythm is maintained over approximately 4 weeks after successful cardioversion. Interestingly, the vast majority of AF recurrences occur during these first few weeks after cardioversion.