In order to test this hypothesis, we will conduct a randomized study comparing the isolation of pulmonary veins without fibrosis imaging (conventional ablation procedure) vs. isolation of the pulmonary veins and pathological (fibrotic) tissue with the aid of LGE-MRI. Fibrotic tissue patches will be encircled and isolated in all patients in the active arm; furthermore, LGE-MRI will be used to identify, locate and guide ablation catheter to anatomical gaps surrounding pulmonary veins in re-do procedures.