|Vein: Coronary sinus|
|Back (posterior) side of the heart, with coronary sinus (blue) labeled.|
|Interior of heart, viewed from the front. Opening of coronary sinus is labeled.|
|Gray's||subject #138 530|
|Source||great cardiac vein|
|Drains to||right atrium|
The coronary sinus is a collection of veins joined together to form a large vessel that collects blood from the heart muscle (myocardium). It delivers deoxygenated blood to the right atrium, as do the superior and inferior vena cava. It is present in all mammals, including humans.
The coronary sinus opens into the right atrium, at the coronary sinus orifice, between the inferior vena cava and the right atrioventricular orifice. It returns the blood from the substance of the heart, and is protected by a semicircular fold of the lining membrane of the auricle, the valve of coronary sinus (or valve of Thebesius). The sinus, before entering the auricle, is considerably dilated - nearly to the size of the end of the little finger. Its wall is partly muscular, and at its junction with the great cardiac vein is somewhat constricted and furnished with a valve consisting of two unequal segments.(Gray 462)
The coronary sinus runs transversely in the groove between the left atrium and left ventricle on the posterior surface of the heart.
The coronary sinus orifice (opening, also known as the ostium of the coronary sinus) is on the posterior, inferior surface of the heart, medial to the inferior vena cava opening, just superior to the septal leaflet of the tricuspid valve. The coronary sinus orifice is guarded by the Thebesian valve.
The coronary sinus 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. It drains into the right atrium.
The anterior cardiac veins do not drain into the coronary sinus but drain directly into the right atrium. Some small veins known as smallest cardiac veins drain directly into any of the four chambers of the heart.
See also 
Additional images 
- -200933319 at GPnotebook
- SUNY Figs 20:04-03 - "Posterior view of the heart."
- MedEd at Loyola Radio/curriculum/Vascular/Coronary_sinus.jpg
- Coronary+sinus at eMedicine Dictionary
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