Persistent left superior vena cava draining into the left atrium is a rare condition. We herein report the case of a 34-year-old male admitted at our institution for paroxysmal atrial fibrillation. Investigations revealed a large ostium secundum atrial septal defect, with a persistent left superior vena cava draining into the left atrium, while the coronary veins drained separately into the left atrium. Surgical correction was performed, closing the defect with a patch and connecting the left superior vena cava to the right atrial appendage with an extra-cardiac conduit.