Location:
The coronary sinus is located in the posterior portion of the coronary sulcus on the diaphragmatic or posterior surface of the heart. The coronary sinus empties directly into the right atrium near the conjunction of the posterior interventricular sulcus and the coronary sulcus (crux cordis area), located between the inferior vena cava and tricuspid valve; this atrial ostium can be partially covered by a Thebesian valve, although the anatomy of this valve is highly variable.
The coronary sinus receives drainage from most epicardial ventricular veins, including the oblique vein of the left atrium (and other left and right atrial veins), the great cardiac vein, the posterior vein of the left ventricle, the left marginal vein, and the posterior interventricular vein. The length of the coronary sinus in adults can vary from 15 to 65 mm.

Function:
The coronary sinus serves as the primary collector of cardiac venous blood.

Importance in cardiovascular diseases:
The delivery of cardioplegia through the coronary sinus has been proven to be safe and effective in myocardial protection, and even superior to the traditional method of antegrade cardioplegia, especially in patients with coronary artery disease.

Importance in device delivery:
Balloon catheters can be placed coronary sinus to deliver therapeutics, cardioplegia buffers, or contrast agents, to obtain venograms of the heart. Numerous device have also been deployed in the coronary sinus as a means to structurally remodel the annulus of the mitral valve (e.g., to minimize valvular regurgitation).