A 47-year-old man with an uncorrected ostium primum atrial septal defect complained of frequent episodes of paroxysmal atrial fibrillation since 1990. Class IC and III antiarrhythmic drugs failed to control the recurrences, and the patient was referred to our institution for electrophysiological evaluation. During the procedure, the focal origin of the atrial fibrillation episodes from the right superior and left pulmonary veins (PVs) was demonstrated by means of multielectrode mapping. For this reason, after selective PV angiography, PV electrical disconnection attempts were performed by delivering low-energy radiofrequency pulses close to the corresponding venoatrial junctions. To facilitate the recognition of electrical PV disconnection, a double-catheter technique was used with a reference quadripolar catheter placed distally in the mapped PV and a quadripolar, 4-mm tip, steerable catheter positioned immediately within the ostium of the same vein for mapping and ablation. Target areas were considered those …