B. Transitional rotors will be ablated After identifying transitional AF rotors, they will be targeted for localized ablation. Rotor location within the atria will be noted, both in the electroanatomic map and relative to the basket catheter splines. Radiofrequency (RF) energy will be applied to the core of the rotor, as described previously6, 9. RF energy will be delivered with a 3.5 mm tip irrigated catheter (ThermoCool, Biosense-Webster) at 25-35 W or, in patients with heart failure, an 8 mm tip catheter (Blazer, Boston Scientific, Marlborough, MA) at 50 to 55 W, with a target temperature of 52˚C. Each lesion is applied for approximately 30-60 seconds, with a predetermined goal of 5-10 minutes of RF energy being placed to cover the ≈2 cm2 area of AF rotor precession.