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How does venous blood from the heart muscle return to the right atrium?

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Silhouette diagram of the human body highlighting the heart and major blood vessels, with labeled arteries in red and veins in blue to show the structure of the cardiovascular system. — Circulatory system Human circulatory system.

Venous blood from the heart muscle returns to the right atrium primarily through the coronary sinus.12

The process occurs as follows:
* Collection: Cardiac veins drain deoxygenated blood from the tissues of the heart muscle.34
* Transport: These veins generally follow the distribution of the distal arteries and travel into the atrioventricular grooves.3
* Drainage: These vessels converge to form the coronary sinus, which serves as the dilated terminal part of the cardiac venous system.23
* Entry: The coronary sinus then empties this venous blood directly into the right atrium.15

This pathway is one of the three major sources of venous return to the right atrium, alongside the superior vena cava and the inferior vena cava, which return blood from the upper and lower body, respectively.1