Although atrial fibrillation is the most common sustained arrhythmia that requires medical attention, it remains a challenge to treat. Nevertheless, considerable progress has been made toward developing curative, catheter-based treatments for selected patients with atrial fibrillation. The most significant clinical observation during electrophysiologic testing in patients with atrial fibrillation has been a recognition of the importance of the pulmonary veins for the initiation of this arrhythmia. In addition to being the most common site of arrhythmogenic foci that trigger the onset of atrial fibrillation, the unique electrophysiologic characteristics of the pulmonary veins may serve to perpetuate established atrial fibrillation. Because of the very short-duration refractory periods that are measured within the pulmonary veins, these structures may serve as a site of high frequency activation due to reentrant activation with small wavelengths. Catheter ablation strategies that are designed to ablate the site of triggering foci with the pulmonary veins have been very successful in selected patients with paroxysmal atrial fibrillation, although the risk of recurrent arrhythmias remains relatively high. In addition, ablation strategies that are designed to electrically isolate the pulmonary veins from the bulk of the left atrium are likely to lead to improvements in the long-term outcome of ablation. For patients with permanent atrial fibrillation, considerable progress has been made in the restoration of sinus rhythm by linear ablation strategies in the left atrium. It is likely that a comprehensive nonpharmacologic treatment for atrial fibrillation will incorporate the lessons learned from each of these approaches and lead to a genuine cure of this vexing arrhythmia. (C) 2000 by Excerpta Medica, Inc.