Coronary Circulation Anatomy: Arterial Supply, Venous Drainage, and Dominance Patterns

Purpose of Coronary Circulation: Why the Myocardium Needs Its Own Vessels

The coronary circulation is the dedicated blood supply and drainage system for the myocardium (heart muscle). Although the heart chambers contain blood, the myocardium cannot rely on that intracavitary blood for oxygen delivery because the endocardium and myocardial thickness create a diffusion barrier. Instead, oxygen and nutrients must be delivered through coronary arteries and removed through coronary veins.

Myocardial oxygen delivery depends heavily on these vessels because the heart has high, continuous metabolic demand and extracts a large fraction of oxygen from arterial blood at baseline. That means increases in myocardial work are met primarily by increasing coronary blood flow (not by extracting much more oxygen). Any narrowing, spasm, or blockage in a coronary artery can therefore reduce oxygen delivery and impair contraction in the territory it supplies.

Arterial Supply: Origins at the Aortic Sinuses

Both coronary arteries originate just above the aortic valve from openings (ostia) in the aortic root:

• Right coronary artery (RCA) arises from the right aortic sinus.
• Left coronary artery (LCA) arises from the left aortic sinus.

Because these ostia sit in the aortic root, coronary perfusion is closely linked to aortic pressure. In practical anatomy terms: trace each coronary artery from the aortic root outward along the epicardial surface, then follow its named branches into grooves (sulci) that guide you to the myocardial regions supplied.

Step-by-step: Finding the Coronary Origins on a Diagram

1. Locate the aortic valve region and the aortic root.
2. Identify the right and left aortic sinuses.
3. Mark the ostia: RCA from right sinus, LCA from left sinus.
4. From each ostium, trace the artery along the atrioventricular (coronary) sulcus and interventricular sulci to predict territories.

Left Coronary Artery System: Left Main, LAD, and Circumflex

The left coronary artery typically has a short trunk called the left main coronary artery (LM), which quickly divides into two major branches:

Continue in our app.

• Listen to the audio with the screen off.
• Earn a certificate upon completion.
• Over 5000 courses for you to explore!

Or continue reading below...

Download the app

• Left anterior descending (LAD), also called the anterior interventricular artery
• Left circumflex (LCx)

Left Main (LM)

The left main is a short conduit between the left aortic sinus and its two main branches. On diagrams, it is the “stem” before the split into LAD and LCx.

LAD (Anterior Interventricular Artery): Course and Common Branches

The LAD runs in the anterior interventricular sulcus toward the apex. It is a key supplier of the anterior wall and much of the interventricular septum.

Common LAD branches include:

• Septal perforators: dive into the interventricular septum to supply the anterior two-thirds of the septum in many hearts.
• Diagonal branches: run obliquely across the anterior surface to supply the anterolateral left ventricle.

LCx (Circumflex): Course and Common Branches

The LCx travels in the left atrioventricular (coronary) sulcus, curving around the left side of the heart toward the posterior surface.

Common LCx branches include:

• Obtuse marginal branches: supply the lateral (left) ventricular wall.
• Atrial branches: supply portions of the left atrium.

Depending on dominance (covered below), the LCx may continue to the crux and contribute to posterior/inferior territories.

Right Coronary Artery (RCA): Course and Common Branches

The RCA runs in the right atrioventricular (coronary) sulcus, passing along the right side of the heart toward the inferior surface. It commonly supplies the right ventricle and, depending on dominance, a variable portion of the inferior left ventricle and posterior septum.

Common RCA branches include:

• Right marginal artery (acute marginal): runs along the right ventricular margin and supplies the right ventricular free wall.
• Posterior descending artery (PDA), also called the posterior interventricular artery (in many hearts): runs in the posterior interventricular sulcus and supplies inferior septal regions and adjacent ventricular walls.
• Small atrial branches: supply parts of the right atrium.

When tracing the RCA on a diagram, look for its path to the “crux” (the junction where the atrioventricular and interventricular grooves meet on the posterior side). The artery that gives rise to the PDA at or near the crux defines coronary dominance.

Coronary Dominance: Defining the PDA Source and Perfusion Territories

Coronary dominance is defined by which coronary artery gives rise to the posterior descending artery (PDA) (posterior interventricular artery). Dominance matters because the PDA supplies important inferior and posterior septal regions; whichever artery gives rise to it typically supplies a larger share of the inferior wall and posterior septum.

Step-by-step: Determining Dominance on a Diagram

1. Find the posterior interventricular sulcus.
2. Identify the artery running in it (the PDA).
3. Trace the PDA backward to its parent vessel at the crux.
4. If it connects to the RCA, label right-dominant; if it connects to the LCx, label left-dominant; if both contribute, label co-dominant.

Practical interpretation: If a heart is left-dominant, the LCx is responsible for a larger inferior territory than in a right-dominant heart. This changes which artery is most critical for perfusion of the inferior wall and posterior septum.

Venous Drainage: Cardiac Veins, Coronary Sinus, and Entry to the Right Atrium

After oxygen is extracted by the myocardium, deoxygenated blood returns via cardiac veins. Most venous blood from the myocardium collects into the coronary sinus, a large venous channel on the posterior aspect of the heart, which then empties into the right atrium.

Major Cardiac Veins (Functional Overview)

• Great cardiac vein: commonly accompanies the LAD on the anterior surface and then continues toward the coronary sinus.
• Middle cardiac vein: commonly accompanies the PDA in the posterior interventricular sulcus and drains into the coronary sinus.
• Small cardiac vein: often runs along the right side (frequently near the RCA/right margin) and drains into the coronary sinus.

Key pathway: myocardial capillaries → cardiac veins → coronary sinus → right atrium.

Step-by-step: Tracing Venous Return from a Myocardial Region

1. Pick a region (e.g., anterior left ventricle).
2. Identify the nearby companion vein (e.g., great cardiac vein near the LAD).
3. Follow the vein toward the posterior side where it joins the coronary sinus.
4. Trace the coronary sinus opening into the right atrium.

Territory Mapping: Typical Arterial Sources by Myocardial Region

Use territory mapping to connect a myocardial region to its most likely arterial source. Remember that individual variation exists, and dominance changes inferior/posterior distributions.

Quick practice: “Name the vessel” prompts

• Anterior interventricular sulcus → LAD (anterior interventricular artery)
• Left atrioventricular sulcus → LCx
• Right atrioventricular sulcus → RCA
• Posterior interventricular sulcus → PDA (from RCA or LCx depending on dominance)

Diagram-Based Practice: Tracing Supply and Drainage Routes

Use a heart diagram (anterior and posterior views) and complete these tracing drills. Work slowly and use arrows.

Practice A: Trace arterial supply to a region

1. Target: anterior LV wall. Start at the left aortic sinus → left main → LAD → diagonal branches → anterior wall.
2. Target: lateral LV wall. Start at the left aortic sinus → left main → LCx → obtuse marginal branches → lateral wall.
3. Target: inferior LV wall. Start at the aortic sinus of the dominant artery → trace to PDA → inferior wall. (First determine dominance by PDA origin.)
4. Target: interventricular septum. Trace LAD → septal perforators for anterior septum; trace PDA for posterior/inferior septum.

Practice B: Trace venous drainage from the same region

1. Anterior LV wall → great cardiac vein → coronary sinus → right atrium.
2. Inferior/posterior region → middle cardiac vein → coronary sinus → right atrium.
3. Right ventricular margin → small cardiac vein (often) → coronary sinus → right atrium.

Practice C: Dominance check integrated with territory

1. Identify the PDA and label its parent vessel (RCA vs LCx).
2. Color the inferior wall territory with the dominant artery’s color.
3. Trace the accompanying vein (often middle cardiac vein) to the coronary sinus and into the right atrium.