Although atrial fibrillation- (AF) induced changes in atrial refractoriness (atrial electrical remodeling) have been demonstrated in a number of different animal models, the clinical significance of this process is unknown. We describe a patient in whom there has been documented progression of atrial ectopy to persistent AF accompanied by evidence of atrial electrical remodeling, with reversal of remodeling following successful ablation of the focal source of AF. A second patient with focal AF, but with a "nonfocal" appearance on the ECG, is also described. These cases illustrate: (1) the possibility that a significant proportion of younger patients with idiopathic persistent AF may well have a focal source as the underlying abnormality; and (2) atrial electrical remodeling reverses following ablation of the underlying source.