The cardiac venous system can be divided into two major parts - the greater and the smaller system.

The greater venous system of the heart consists of veins that mainly drain most of the outer myocardium. The main veins of this system are the coronary sinus and its tributaries, the anterior cardiac veins, the ventricular septal and atrial veins, that are all intercommunicating.

Most cardiac veins drain into the coronary sinus, which is positioned in the posterior atrioventricular groove between the left atrium and ventricle. The sinus opens into the right atrium. The opening is located between the opening of the inferior vena cava and the right atrioventricular opening.

The main tributaries to the coronary sinus include the great, middle and small cardiac veins, the oblique vein of the left atrium, and the inferior vein of the left ventricle.

The great cardiac vein starts at the cardiac apex, ascends in the anterior interventricular groove, then follows the right atrioventricular groove, passes to the left and posteriorly, and enters the coronary sinus at its origin site.

The middle cardiac vein also starts at the apex, passes posteriorly in the inferior interventricular groove and enters the coronary sinus near its atrial end.

The small cardiac vein - lies in the posterior atrioventricular groove and opens in the coronary sinus at its atrial end.

The oblique vein of the left atrium - descends obliquely on the posterior side of the left atrium and enters the coronary sinus.

The inferior vein of the left ventricle (previously known as the posterior vein of the left ventricle) - situated on the diaphragmatic surface of the left ventricle, usually enters the middle of the coronary sinus, but sometimes joins the great cardiac vein.

All these veins except for the oblique vein have valves covering their openings.

The anterior cardiac veins are usually two or three (up to five) vessels that collect venous blood from the anterior part of the right ventricle. These veins ascend in the subepicardial tissue and pass the right part of the atrioventricular groove, ending in the right atrium.

The smaller venous system mainly consists of the small cardiac (Thebesian) veins that mainly drain the inner myocardial walls and open into all of the cardiac chambers.

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Coronary veins