Location:
The ostium of the left marginal vein is typically at the distal end of the coronary sinus. In most human hearts we have observed a valve associated with the ostium as this venous drainage enters the coronary sinus.

Function:
This cardiac vein returns deoxygenated blood (metabolic waste products) from the lateral wall of the left ventricle.

Importance in device delivery:
Left heart pacing can be achieved via placing leads into the left marginal vein; in the diseased heart this region of the heart will often be the region of latest ventricular depolarization.