Stable rotor source for human atrial fibrillation (AF), adjacent to moderate complex fractionated atrial electrograms (CFAE). A, Left atrial rotor during AF. B, Activation emanates from rotor to surrounding atrium during AF. C, Rotor precesses over time along the color-coded time line (Movie I in the online-only Data Supplement). D, Electrograms at various sites, referenced to E. E, Panoramic CFAE/AF source map showing AF rotor adjacent to moderate CFAE (grades 8–10), but with higher grade CFAE at distant sites. F, CFAE surrounds AF rotor precession by <180°. G, Focal impulse and rotor modulation (FIRM) ablation at the rotor terminates AF to sinus rhythm hyperacutely in <1 minute before any other ablation. CFAE on the ablation catheter extinguishes as AF terminates. Orientation: the left atrium is opened horizontally across the mitral value with the valve halves folded up and down. The right atrium is opened vertically through the tricuspid value with the valve halves folded laterally and septally.