 - Design: Double blind and single center study, in which patients will be randomly assigned to a cardioversion group using intravenous flecainide or to an atria-preferential and atrial-specific blockade group using intravenous vernakalant. Patients will be routinely monitored in the electrophysiology room for 90 minutes upon drug administration to acquire both 12-lead digitized ECG signals and non-invasive body surface potential mapping. Body surface recordings and conventional ECG signals will be exported to obtain temporal and spectral parameters of atrial activity during AF, and measure organization and atrial rate in both groups of patients undergoing pharmacological cardioversion. The success rate of cardioversion obtained in both groups will be correlated with the patterns of activation and spectral parameters obtained from the body surface, which will provide what type of paroxysmal AF episodes are suitable to terminate upon administration of anti-arrhythmic drugs with an atrial specific and atria-preferential profile. 