left marginal vein left marginal vein the left marginal vein is a vein of the heart which courses near or over the left margin of the heart. it drains venous blood from much of the myocardium of the left ventricle. it usually empties into the great cardiac vein (but may sometimes instead drain into the coronary sinus directly). left marginal veinbase and diaphragmatic surface of heart. (left marginal vein labeled at center left.)detailsdrains fromleft ventricledrains togreat cardiac veinarteryleft marginal arteryidentifierslatinvena marginalis sinistrata98a12.3.01.005ta24161fma4708anatomical terminology along its course, it is accompanied by a marginal branch of the left coronary artery (the arterial branch running deep to the left marginal vein).