The cardiac veins carry deoxygenated blood from the myocardium to the right atrium.

• Cardiac veins are classified by their blood-flow return to the heart:
  • The coronary sinus (and its four major tributaries) drains into the right atrium.
  • The anterior cardiac veins drain directly into the right atrium.
  • The small cardiac veins drain directly into the nearest chamber.

Pathway of venous return to the coronary sinus:

The coronary sinus is a wide, short vessel that drains directly into the right atrium. It runs in the posterior coronary sulcus.

• Four major tributaries:
  • Great cardiac vein
  • Left posterior ventricular vein
  • Middle cardiac vein
  • Small cardiac vein

Anterior interventricular vein

• Arises near the apex of the heart and travels superiorly (within the anterior interventricular sulcus).
• Once it reaches the coronary sulcus, the anterior interventricular vein becomes the great cardiac vein.
  • Travels posteriorly to drain directly into the left end of the coronary sinus (be aware that some texts do not name the anterior interventricular vein separately; instead, they refer to this entire vessel as the great cardiac vein).

Right marginal vein

• Travels superiorly along the right side of the heart.
• At the coronary sulcus, the right marginal vein becomes the small cardiac vein.
  • Wraps posteriorly to drain directly into the right end of the coronary sulcus (in some individuals, the right marginal vein drains directly into the right atrium).

Middle cardiac vein

• Arises near the apex and runs in the posterior interventricular sulcus (hence, it is also called the posterior interventricular vein).

Left posterior ventricular vein

• Arises between the great and middle cardiac veins.

Anterior cardiac veins

• Arise on the superior surface of the right ventricle, and drain directly into the right atrium.

Smallest cardiac veins

aka, venae cordis minimae, aka, thebesian veins

• Valveless vessels that drain directly into the cardiac chambers, particularly the right atrium.

Vein – Artery Associations:

• The anterior interventricular vein travels with the anterior interventricular artery.
• The middle cardiac vein travels with the posterior interventricular artery.
• The small cardiac vein travels with the right coronary artery.
• The right marginal vein travels with the right marginal artery.

In Summary:

The great cardiac and left posterior ventricular veins drain regions of the myocardium supplied by the left coronary artery;
The middle and small cardiac veins drain regions of the myocardium supplied by the right coronary artery.