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Other Terms: Sinus coronarius, Sinus coronaire
The coronary sinus is the continuation of the great cardiac vein, greatly increased in size; it is about two and a half centimeters (one inch) long. It collects blood from the myocardium of the heart, and into it empty the left marginal vein, posterior vein of the left ventricle, and the small, middle, great, and oblique cardiac veins. It delivers deoxygenated blood to the right atrium along with both the superior vena cava and the inferior vena cava. The coronary sinus is situated in the right atrium above and posterior to the ventricles, and runs along the posterior surface of the heart in the coronary sulcus. It then empties into the right atrium on the posterior, inferior surface, and medial to the inferior vena cava; its orifice is guarded by the valve of the coronary sinus, or Thebesian valve. The sinus is dilated at the back of its opening, but is constricted at its junction with the great coronary vein, where two unequal valvular segments prevent regurgitation.