Right cardiac veins

The right cardiac veins (venae cordis dextrae) are small, valveless veins that drain deoxygenated blood from the myocardium mainly of the right ventricle, but few also from the right atrium. They convey it directly into the right atrium, rather than passing through the coronary sinus. They run over the surface of the right ventricle and vary in number and size, forming part of the cardiac venous return system by providing an additional pathway for venous drainage from the right side of the heart.

In carnivores, the main ventricular branch, the right marginal vein of heart, may joint other anterior ventricular branches and right atrial branches to form the small cardiac vein that directly drains in the right atrium (in humans, the small cardiac vein follows the right coronary sulcus to drain into the coronary sinus).