Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
The coronary sinus is a collection of veins joined together to form a large vessel that collects blood from the myocardium of the heart. It is present in humans and other animals.
It is located between the left atrium and ventricle on the posterior surface of the heart.
It runs transversely in the groove between the left atrium and ventricle on the posterior surface of the heart.
The coronary sinus orifice (opening) is just superior to the septal leaflet of the tricuspid valve. The coronary sinus orifice is also known as the ostium of the coronary sinus.
It receives blood mainly from the small, middle, great and oblique cardiac veins. It also receives blood from the left marginal vein and the left posterior ventricular vein. The anterior cardiac veins drain directly into the right atrium. (Some small veins drain into any of the four chambers of the heart.)
It drains into the right atrium on the posterior, inferior surface, medial to the inferior vena cava opening.
- Template:SUNYAnatomyFigs - "Posterior view of the heart."
The coronary sinus can be the site of drainage of an atrial septal defect (see coronary sinus atrial septal defect).