Largest vein of heart; drains most myocardial venous blood into right atrium; lies in posterior coronary sulcus.

Position

• Left posterior coronary sulcus, diaphragmatic surface
• Between left atrium (above) + left ventricle (below)
• Covered partly by muscular fold of left atrium

Course

• Runs left → right in posterior atrioventricular groove
• ~3 cm long
• Continuation of great cardiac vein after it receives oblique vein of left atrium

Termination

• Opens into right atrium, posterior wall, between IVC opening + right AV orifice
• Guarded by valve of coronary sinus (Thebesian valve) — rudimentary, non-functional

Tributaries (G-M-S-P-O)

Great cardiac vein — begins near apex → ascends anterior interventricular sulcus with LAD → turns left in coronary sulcus with circumflex → continues as coronary sinus (largest tributary)

Middle cardiac vein — begins near apex → ascends posterior interventricular sulcus with posterior interventricular artery → middle part of sinus

Small cardiac vein — right AV groove, with RCA → right end of sinus; may receive right marginal vein

Oblique vein of left atrium (vein of Marshall) — small, posterior LA surface; develops from left common cardinal vein

Persistence of left common cardinal vein → persistent left SVC draining into coronary sinus → dilated coronary sinus

Variable Tributaries

• Left marginal vein → great cardiac vein or coronary sinus
• Right marginal vein → small cardiac vein or directly right atrium

NOT Draining into Coronary Sinus

Anterior cardiac veins — 3-4 small veins, anterior right ventricle surface, open directly into right atrium

Venae cordis minimae (Thebesian veins) — smallest cardiac veins; in walls of all chambers; open directly into chamber of origin; more numerous in right atrium/ventricle

Those opening into left atrium/ventricle contribute small physiological right-to-left shunt

Applied Anatomy

• Cardiac resynchronisation therapy — pacing lead through coronary sinus into tributary to pace LV
• Retrograde cardioplegia — cardioplegic solution via coronary sinus cannula during surgery
• Persistent left SVC — commonly drains into coronary sinus → dilated sinus; relevant in central venous catheterisation/device placement

The coronary sinus is the largest vein of the heart. It drains most venous blood from the myocardium into the right atrium and lies in the posterior part of the coronary sulcus.

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Position

The coronary sinus lies in the left posterior part of the coronary sulcus on the diaphragmatic surface of the heart.

It lies between:

• Left atrium above
• Left ventricle below

It is covered partly by a muscular fold of the left atrium.

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Course

The coronary sinus runs from left to right in the posterior atrioventricular groove.

It is about 3 cm long.

It is commonly described as the continuation of the great cardiac vein after it receives the oblique vein of the left atrium.

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Termination

The coronary sinus opens into the right atrium.

Site of opening:

• Posterior wall of right atrium
• Between the opening of the IVC and the right atrioventricular orifice

Valve:

• Guarded by the valve of coronary sinus, also called the Thebesian valve
• The valve is rudimentary and non-functional

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Tributaries of Coronary Sinus

Main tributaries are remembered as:

G-M-S-P-O

Great, Middle, Small, Posterior, Oblique

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Great Cardiac Vein

Course:

1. Begins near apex.
2. Ascends in anterior interventricular sulcus with LAD.
3. Turns left in coronary sulcus with circumflex artery.
4. Continues as coronary sinus.

It is the largest tributary of the coronary sinus.

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Middle Cardiac Vein

• Begins near apex.
• Ascends in posterior interventricular sulcus.
• Accompanies posterior interventricular artery.
• Opens into the middle part of coronary sinus.

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Small Cardiac Vein

• Runs in right atrioventricular groove.
• Accompanies right coronary artery.
• Opens into the right end of coronary sinus.
• May receive right marginal vein.

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Posterior Vein of Left Ventricle

• Runs on diaphragmatic surface of left ventricle.
• Opens into coronary sinus.

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Oblique Vein of Left Atrium

The oblique vein of left atrium is also called the vein of Marshall.

Features:

• Small vein on posterior surface of left atrium.
• Opens into left end of coronary sinus.
• Develops from the left common cardinal vein.

Clinical developmental point:

• Persistence of the left common cardinal vein may form a persistent left superior vena cava draining into the coronary sinus.
• This can produce a dilated coronary sinus.

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Variable Tributaries

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Cardiac Veins Not Draining into Coronary Sinus

Most cardiac venous blood drains through the coronary sinus, but two groups bypass it.

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Anterior Cardiac Veins

Features:

• Usually 3-4 small veins.
• Run over anterior surface of right ventricle.
• Open directly into the right atrium.
• Do not drain into coronary sinus.

They are important because they drain part of the right ventricle independently.

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Venae Cordis Minimae

Also called:

• Thebesian veins
• Smallest cardiac veins

Features:

• Very small veins in the walls of all chambers.
• Open directly into the chamber in which they lie.
• More numerous in right atrium and right ventricle.

Physiological point:

• Thebesian veins opening into the left atrium or left ventricle contribute a small amount to the normal physiological right-to-left shunt and slight venous admixture.

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Summary of Cardiac Venous Drainage

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Clinical Importance

Cardiac Resynchronisation Therapy

In heart failure with conduction delay, a pacing lead may be passed through the coronary sinus into a tributary vein to pace the left ventricle.

Anatomical knowledge of the coronary sinus and its tributaries is important for lead placement.

Retrograde Cardioplegia

During cardiac surgery, cardioplegic solution may be delivered retrogradely through a cannula in the coronary sinus to protect myocardium.

Persistent Left Superior Vena Cava

If the left superior vena cava persists, it commonly drains into the coronary sinus.

Effects:

• Dilated coronary sinus
• Important during central venous catheterisation and cardiac device placement
• May be detected on imaging or echocardiography

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