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. History of presentation A 34-year-old male was admitted to our hospital following the sudden onset of palpitation and shortness of breath. His past medical history, otherwise unremarkable, included hypertension and overweight (BMI 28.2 Kg/m 2). Physical examination revealed clubbing and low SpO 2 (90%). Investigations Electrocardiogram revealed atrial fibrillation, which reverted spontaneously to sinus rhythm. Transthoracic echocardiogram revealed a large ostium secundum atrial septal defect (ASD), 41x42mm in size, with left-toright shunt, pulmonary hypertension (60mmHg) and dilatation of the right ventricle. Computed tomography (CT) scan showed: (1) a persistent left superior vena cava (LSVC) draining into the left atrium (LA) in close proximity to the left atrial appendage, (2) the absence of a left brachiocephalic vein, (3) the abnormal independent drainage of the coronary veins in the LA. The great cardiac vein drained into the postero-lateral wall, the marginal vein into the lower wall and two middle cardiac veins into the medial-lower wall of the LA (Fig. 1; Fig 2). Cardiac catheterisation confirmed pulmonary hypertension (pulmonary arterial pressure 70/44mmHg; mean 45mmHg, wedge pressure 14mmHg), arterial SpO2 91%, systemic venous saturation 70% and pulmonary artery saturation 90%, Qp/Qs 2.8. Nitric oxide caused a significant reduction of pulmonary artery and wedge pressures, with an increment of the Qp/Qs to 11.5. The patient was referred and accepted for elective surgery. Management Surgery was performed through full median sternotomy. The absence of the left brachiocefalic vein was confirmed. The LSVC entered the LA cephalad and medial to the left superior pulmonary vein (Fig 3 and