Left atrial muscle sleeves extending over the pulmonary veins are critical to the initiation of atrial fibrillation (AF) in some patients. This report describes two patients with paroxysmal AF who demonstrate widely-split pulmonary vein (PV) double potentials at the pulmonary vein ostium during sinus rhythm. The response by the double potentials to PV isolation is also characterized. These cases emphasize the importance of recognizing unusual PV electrophysiology and using patient- and mechanism-specific approaches to catheter ablation for AF.