A persistent left superior vena cava (PLSVC) is thoracic system variation in which the left-sided vena cava fails to involute during normal development. It is the most common variation of the thoracic venous system, occurring in approximately 0.3% of the population. The abnormality is often detected on pre-operative imaging studies, but may also be discovered intra-operatively. A PLSVC may make it difficult to achieve proper venous drainage or deliver of retrograde cardiopledgia. Management of a PLSVC during CPB depends on factors such as the size and drainage site of the PSLVC.