Corpus: Cardiac vein

Cardiac veins are blood vessels that carry deoxygenated blood away from the heart muscle.

The large cardiac veins run parallel to the coronary arteries over long distances, which is why they are also called coronary veins. However, they make up only part of the system that returns blood to the heart. The venous return from the heart is divided into three systems:

2.1. Coronary Sinus system

The coronary sinus system includes the cardiac veins that drain into the right atrium via the coronary sinus, responsible for carrying about 75 % of the heart’s venous blood. It consists of the following veins:

• Great cardiac vein: Runs alongside the left coronary arteries and their branches.
  • Anterior interventricular vein: Accompanied by septal veins.
  • Left marginal vein: Drains blood from the left margin of the heart.
  • Posterior vein of the left ventricle: Drains the posterior part of the left ventricle.
• Middle cardiac vein (Posterior interventricular vein): Runs in the posterior interventricular groove.
• Oblique vein of the left atrium (Marshall vein): Located at the back of the left atrium, near the left pulmonary veins. In 2 % of cases, it forms the superior vena cava, which drains into the coronary sinus.
• Small cardiac vein: Present in about 50 % of cases, it runs along the posterior portion of the right coronary groove, collecting blood from nearby ventricular and atrial areas.

2.2. Transmural system

This system includes smaller veins on the surface of the heart that penetrate the heart wall and open directly into the right atrium near the tricuspid valve. These veins include:

• Anterior cardiac veins: These veins drain the anterior sections of the right atrium and adjacent parts of the right ventricle. They open directly into the right atrium above the tricuspid valve.
• Epicardial atrial veins: These veins drain the posterior and interatrial regions of the atrium and typically empty into the right atrium, though they can also drain into the superior vena cava, coronary sinus, or left atrium.

2.3. Endomural system

The endomural system consists of the smallest cardiac veins, known as Thebesian Veins. These veins arise from the innermost layer of the heart muscle (myocardium) and open directly into the heart chambers.

Additionally, blood from small myocardial arteries can bypass veins entirely, flowing directly into the ventricles without passing through a venous segment