[An unusual cause of right-left shunt: anastomosis of the left superior vena cava with the left atrium].

We report the case of a 73 year old man presenting with severe hypoxaemia due to an anatomical right to left shunt from a persistent left superior vena cava (VCSG) anastomosing with the left auricle. This was fortuitously discovered while placing a left sub clavicular catheter; the diagnosis of the VCSG draining into the left auricle was confirmed by superior phlebography and CT scanning. The discovery of this shunt after a pulmonary embolus suggested to us that the rise in venous pressure secondary to the embolus led to both clinical symptoms and hypoxaemia from the shunt, which had until then been clinically silent. No surgical treatment was performed.