Persistent left superior vena cava is the most common thoracic venous anomaly seen in approximately 0.3% of normal popultaion. During the embryonic life it is the counterpart of normal right sided superior vena cava which fails to obliterate.

In most of the cases, it drains into the coronary sinus while in less than 8% cases it is seen draining into the left atrium thus creating a small right to left shunt.