Flecainide was chosen for antiarrhythmic treatment in the Flec-SL trial because it is effective in the prevention of recurrent AF after cardioversion in the absence of major structural heart disease, has been safe as an outpatient treatment for recurrent AF, and prolongs the atrial action potential in patients with AF. In addition to its action potential-prolonging effect, flecainide induces post-repolarization refractoriness in the atria, an electrophysiological effect that may assist in the prevention of recurrent AF.