Oblique vein of left atrium

The oblique vein of the left atrium (Vein of Marshall), is an embryonic remnant that represents a small venous structure draining the posterior surface of the left atrium. It extends from the coronary sinus at its junction with the great cardiac vein, continuing into the lateral ridge of left atrium, the vestigial fold between the left pulmonary veins and the left atrial appendage.

The oblique vein is present in approximately 85-99% of individuals, though it may be poorly developed in many cases. The vein has a mean diameter of 0.4-1.8 mm (or approximately 1.23 mm in some studies) and a mean length of approximately 36.5 mm, though this is highly variable. It courses along the posterior surface of the left atrium in the direction of the left superior pulmonary vein. The vein's ostium opens into the coronary sinus at a mean distance of approximately 30.9 mm from the coronary sinus ostium and is typically located adjacent to the Vieussens valve when present.