Cardiac Veins

Cardiac veins form the venous drainage system of the heart. They collect deoxygenated blood from the myocardium and return it primarily to the right atrium. Most cardiac venous blood passes through the coronary sinus, a large venous channel situated on the posterior aspect of the heart.

The principal veins associated with the coronary sinus include the great cardiac vein, middle cardiac vein, small cardiac vein, posterior vein or veins of the left ventricle, and the oblique vein of the left atrium. Other venous channels, particularly the anterior cardiac veins and smallest cardiac veins, can drain directly into cardiac chambers without first entering the coronary sinus.

Organization of Cardiac Venous Drainage

Venous drainage of the heart can be divided into three major pathways:

• Veins draining into the coronary sinus
• Anterior cardiac veins draining directly into the right atrium
• Smallest cardiac veins draining directly into the cardiac chambers

Major Cardiac Veins

Vein	Typical Course or Territory	Drainage
Great cardiac vein	Anterior interventricular sulcus, then coronary sulcus	Coronary sinus
Middle cardiac vein	Posterior interventricular sulcus	Coronary sinus
Small cardiac vein	Along right margin and right part of coronary sulcus	Coronary sinus
Posterior vein of left ventricle	Posterior surface of left ventricle	Coronary sinus
Oblique vein of left atrium	Posterior left atrium	Coronary sinus
Anterior cardiac veins	Anterior right ventricle	Directly into right atrium
Smallest cardiac veins	Within myocardial walls	Directly into cardiac chambers

Coronary Sinus

The coronary sinus is the principal venous channel of the heart. It lies in the posterior part of the coronary sulcus, also called the atrioventricular groove, between the left atrium and left ventricle.

It receives most of the major cardiac veins and opens into the right atrium.

Opening of the Coronary Sinus

The coronary sinus opens into the posterior-inferior region of the right atrium, between the opening of the inferior vena cava and the right atrioventricular orifice.

The opening may be partly guarded by the valve of the coronary sinus, also known as the valve of Thebesius.

Formation of the Coronary Sinus

The coronary sinus begins toward the left side of the posterior coronary sulcus, where the great cardiac vein continues into the enlarged venous channel.

It then courses toward the right along the posterior atrioventricular groove before entering the right atrium.

Tributaries of the Coronary Sinus

Major tributaries commonly include:

• Great cardiac vein
• Middle cardiac vein
• Small cardiac vein
• Posterior vein or veins of the left ventricle
• Oblique vein of the left atrium

Great Cardiac Vein

The great cardiac vein is one of the largest veins draining the myocardium. It begins near the apex of the heart and ascends in the anterior interventricular sulcus.

In this region it accompanies the anterior interventricular artery, commonly known clinically as the left anterior descending artery.

Course of the Great Cardiac Vein

After ascending in the anterior interventricular sulcus, the great cardiac vein turns toward the left and passes around the left side of the heart within the coronary sulcus.

It continues posteriorly and becomes continuous with the coronary sinus.

Drainage Territory of the Great Cardiac Vein

The great cardiac vein receives blood from territories that include substantial portions of the anterior heart and left ventricular myocardium.

Its tributaries accompany branches of the left coronary arterial system in several regions.

Anterior Interventricular Relationship

Within the anterior interventricular sulcus, the great cardiac vein lies in close association with the anterior interventricular artery.

This artery-vein relationship is an important landmark on the sternocostal surface of the heart.

Middle Cardiac Vein

The middle cardiac vein, also called the posterior interventricular vein, begins near the apex and ascends along the diaphragmatic surface of the heart.

It runs within the posterior interventricular sulcus.

Relationship to the Posterior Interventricular Artery

The middle cardiac vein accompanies the posterior interventricular artery within the posterior interventricular sulcus.

It terminates in the coronary sinus near its right atrial end.

Drainage Territory of the Middle Cardiac Vein

The middle cardiac vein drains myocardium associated with the posterior and inferior regions of the ventricles and the interventricular region.

Its exact tributary pattern varies among individuals.

Small Cardiac Vein

The small cardiac vein drains portions of the right side of the heart.

It commonly courses along the right margin of the heart before entering the right portion of the coronary sulcus.

Relationship to the Right Coronary Artery

In the coronary sulcus, the small cardiac vein is associated with the right coronary artery.

It typically continues posteriorly and drains into the coronary sinus.

Right Marginal Vein

A vein accompanying the right marginal artery may contribute to the small cardiac vein.

Venous anatomy in this region is variable, and the right marginal venous channel may have different drainage patterns.

Posterior Vein of the Left Ventricle

The posterior vein of the left ventricle drains the posterior surface of the left ventricular myocardium.

One or more veins may ascend across the posterior left ventricle and empty into the coronary sinus.

Oblique Vein of the Left Atrium

The oblique vein of the left atrium is a small vein descending across the posterior surface of the left atrium.

It joins the coronary sinus near its left end.

Embryological Relationship of the Oblique Vein

The oblique vein of the left atrium is a remnant associated with the embryonic left common cardinal venous system.

Its developmental relationship is continuous with that of the coronary sinus, which also derives from structures of the embryonic venous system.

Anterior Cardiac Veins

The anterior cardiac veins are small veins that drain the anterior wall of the right ventricle.

Unlike most major cardiac veins, they generally do not empty into the coronary sinus.

Direct Drainage Into the Right Atrium

Anterior cardiac veins cross the coronary sulcus and open directly into the right atrium.

This provides an important alternative pathway for cardiac venous return.

Smallest Cardiac Veins

The smallest cardiac veins, traditionally called the venae cordis minimae or Thebesian veins, are minute venous channels within the myocardium.

They open directly from myocardial tissue into the cardiac chambers.

Distribution of the Smallest Cardiac Veins

Smallest cardiac veins occur in all four chambers but are especially associated with the right-sided chambers.

They provide direct communication between the myocardial venous circulation and the cavities of the heart.

Physiological Effect of Direct Venous Drainage

Small venous channels opening directly into the cardiac chambers contribute to normal physiological mixing of blood.

Those entering the left-sided chambers contribute a small amount of deoxygenated blood to otherwise oxygenated systemic arterial blood.

Venous Drainage of the Right Atrium

The right atrial myocardium is drained through small cardiac venous channels, including smallest cardiac veins and other local tributaries.

The coronary sinus itself terminates within the right atrium but primarily carries venous blood collected from other regions of the heart.

Venous Drainage of the Right Ventricle

The right ventricle is drained through several pathways.

The small cardiac vein, anterior cardiac veins, and smallest cardiac veins all contribute to venous drainage of right ventricular myocardium.

Venous Drainage of the Left Ventricle

The left ventricular myocardium is drained extensively by tributaries of the great cardiac vein, posterior veins of the left ventricle, and the middle cardiac vein.

Most of this blood ultimately reaches the right atrium through the coronary sinus.

Venous Drainage of the Left Atrium

Venous drainage of the left atrial myocardium includes small venous channels and the oblique vein of the left atrium.

Some minute veins may drain directly into the chamber.

Relationship to Coronary Arteries

Several major cardiac veins accompany coronary arteries within grooves on the surface of the heart.

These paired relationships provide useful anatomical landmarks.

Major Artery-Vein Relationships

Cardiac Vein	Associated Artery	Location
Great cardiac vein	Anterior interventricular artery	Anterior interventricular sulcus
Middle cardiac vein	Posterior interventricular artery	Posterior interventricular sulcus
Small cardiac vein	Right coronary artery in part of its course	Right coronary sulcus

Epicardial Location

Major coronary vessels travel within connective tissue beneath the visceral layer of serous pericardium, or epicardium.

Epicardial fat commonly surrounds the vessels as they pass through the coronary and interventricular sulci.

Venous Valves

Valves may occur within portions of the cardiac venous system, although their distribution is variable.

The coronary sinus ostium may be partly covered by the valve of the coronary sinus, and valves may occur at some tributary junctions.

Variation in Cardiac Veins

Cardiac venous anatomy shows substantial individual variation.

The size, number, continuity, and drainage patterns of individual veins can differ, which is clinically important when cardiac venous anatomy is used for catheter-based procedures.

Coronary Venous Blood Flow

Cardiac venous return reflects blood that has passed through the coronary microcirculation and supplied the myocardium.

Most of this blood returns through the coronary sinus, although direct venous channels account for a smaller portion.

Coronary Sinus and Right Atrium

The coronary sinus provides the principal route by which venous blood from the myocardium enters the right atrium.

From the right atrium, this blood joins systemic venous return and subsequently passes through the right ventricle into the pulmonary circulation.

Clinical Significance

Coronary Sinus Catheterization

The coronary sinus can be entered from the right atrium using specialized catheters.

Its position and tributaries make it an important route in several diagnostic and therapeutic cardiac procedures.

Cardiac Resynchronization Therapy

In cardiac resynchronization therapy, a pacing lead intended to stimulate the left ventricle is commonly advanced through the coronary sinus into an appropriate cardiac venous branch.

The anatomy and size of coronary sinus tributaries can therefore directly affect lead placement.

Coronary Venous Anatomy and Device Placement

Variation in cardiac veins can make transvenous lead placement technically challenging.

Venous diameter, branching angles, valves, tortuosity, and available target veins may influence procedural strategy.

Retrograde Cardioplegia

During some cardiac operations, cardioplegic solution can be delivered through the coronary sinus in a retrograde direction.

This technique uses the cardiac venous system to distribute cardioplegia through portions of the myocardium.

Coronary Sinus Enlargement

An enlarged coronary sinus may be associated with altered venous drainage or increased pressure within connected venous pathways.

Its appearance can provide clues to congenital or acquired cardiovascular abnormalities.

Persistent Left Superior Vena Cava

A persistent left superior vena cava commonly drains into the coronary sinus.

This can produce marked enlargement of the coronary sinus and is important during central venous access, electrophysiological procedures, and cardiac device implantation.

Coronary Sinus Thrombosis

Thrombosis of the coronary sinus is uncommon but can interfere with myocardial venous drainage.

It may occur in association with invasive procedures, devices, hypercoagulable states, or other cardiac conditions.

Coronary Sinus Sampling

Blood obtained from the coronary sinus can provide information about substances released or extracted by the myocardium.

Coronary sinus sampling has therefore been used in physiological and specialized clinical investigations of cardiac metabolism.

Cardiac Venous Drainage Summary

Drainage Route	Destination
Great cardiac vein	Coronary sinus
Middle cardiac vein	Coronary sinus
Small cardiac vein	Coronary sinus
Posterior vein of left ventricle	Coronary sinus
Oblique vein of left atrium	Coronary sinus
Anterior cardiac veins	Right atrium directly
Smallest cardiac veins	Cardiac chambers directly

Key Features of the Cardiac Veins

Feature	Key Point
Primary function	Drain venous blood from the myocardium
Principal collecting channel	Coronary sinus
Final major destination	Right atrium
Largest major tributary	Great cardiac vein
Posterior interventricular vein	Middle cardiac vein
Direct right atrial drainage	Anterior cardiac veins
Direct chamber drainage	Smallest cardiac veins
Clinical importance	Provides access for pacing leads and other cardiac procedures

Anatomical Importance

The cardiac veins form an extensive drainage network that parallels many of the arterial pathways supplying the myocardium. Their arrangement ensures that blood passing through the coronary capillary circulation can return efficiently to the right side of the heart.

The coronary sinus is the dominant collecting channel, but the presence of anterior cardiac veins and smallest cardiac veins means that not all myocardial venous blood follows this route. These alternative pathways are an important feature of cardiac venous anatomy.

The close relationships between cardiac veins, coronary arteries, cardiac sulci, and the right atrium make the venous system important not only for understanding normal coronary circulation but also for cardiac imaging, electrophysiology, resynchronization therapy, cardiac surgery, and other invasive procedures.