Aims Radiofrequency ablation targeting the pulmonary veins offers potential cure for patients with symptomatic paroxysmal atrial. fibrillation (AF). Initiating ectopics can also arise from other sites including the major thoracic veins, vein of Marshall and more rarely, persistent left superior vena cava (LSVC). We report our experience with arrhythmogenic persistent LSVC initiating AF.Methods and results The LSVC was present in four patients from an overall series of 204 patients undergoing AF ablation at our centre. All were mates, mean age 50 +/- 11 years. All patients underwent pre-procedure transesophageal echocardiography. The mapping of the LSVC was performed with a circumferential mapping catheter following pulmonary vein isolation. Atrial. ectopics from the LSVC were observed to initiate AF Catheter ablation (power controlled mode; 65 degrees C and 30 W at irrigation flow rate of 30 mL/min) resulted in electrical. isolation of the LSVC in all patients and was accompanied by termination of AF in one of four patients. There were no complications. All. patients underwent multiple procedures (three procedures in one patient, two procedures in three patients). After a mean follow-up of 18 +/- 7 months (range 7-24 months), three of the four patients remained free of AF off antiarrhythmic medications.Conclusion Arrhythmogenic foci within persistent LSVC can result in AF despite electrical isolation of pulmonary veins. This report demonstrates the importance of the LSVC as a potential source of atrial. ectopics initiating and perpetuating AF.