In brief, the investigators start patients with persistent AF on dofetilide 3 months prior to scheduled ablation. In 96% of patients, AF either suppresses completely or is transformed into a paroxysmal pattern. The net effect is "reverse remodeling" of the left atria. The investigators have confirmed this by using a reduction in P wave duration as a surrogate of remodeling. At the ablation procedure, the investigators perform PVI alone.