Persistent left superior vena cava.

Abstract Three cases of persistent bilateral superior venae cavae diagnosed by cardiac catheterization have been presented. The embryologic development of the superior venae cavae has been reviewed. When the left superior vena cava empties into the right atrium via the coronary sinus, there is no change in circulatory dynamics such as occurs when drainage is to the left atrium. The practical significance of a persistent left superior vena cava is considered.