 - The investigators will include patients without structural heart disease and short-lasting AF episodes 48 h.. 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 to acquire both 12-lead digitized ECG signals and non-invasive body surface potential mapping. Atrial signals will be extracted from both the multisite body surface and ECG recordings to obtain temporal and spectral parameters, and measure organization and atrial rate in both groups. The results obtained in the clinical setting will be studied in mathematical models to understand their capability to terminate paroxysmal AF. The project expects to provide consistent, reliable and reproducible parameters that will assist clinicians to know what type of paroxysmal AF episodes will be more suitable to effectively terminate, upon administration of drugs with an atrial specific and atria-preferential profile. 