🎓 Prepared by students from Boğaziçi University

What is Coronary Circulation?

Coronary circulation is the network of blood vessels that supplies oxygen and nutrients to the heart muscle (myocardium) itself. It begins at the very first branches off the aorta and drains back into the right atrium.

Short answer

Coronary circulation is the blood supply to the heart wall, delivered by the left and right coronary arteries branching from the aorta and drained by cardiac veins into the coronary sinus, which empties into the right atrium.

Path of coronary blood flow

1
Aortic root
Left and right coronary arteries branch off just above the aortic valve
↓
2
Left coronary artery
Splits into the LAD (anterior wall) and circumflex (lateral wall) branches
↓
3
Right coronary artery
Supplies the right ventricle and, in most people, the inferior wall and SA/AV nodes
↓
4
Myocardial capillaries
Oxygen and nutrients diffuse into heart muscle cells
↓
5
Cardiac veins
Deoxygenated blood drains into the great, middle and small cardiac veins
↓
6
Coronary sinus → right atrium
Cardiac veins converge into the coronary sinus, which empties directly into the right atrium

Step-by-step worked examples

At rest, coronary blood flow is about 5% of total cardiac output. If cardiac output is 5,000 mL/min, how much blood flows through the coronary arteries?

Coronary flow = 5% × Cardiac output
Coronary flow = 0.05 × 5,000 mL/min
Coronary flow = 250 mL/min

The left anterior descending (LAD) artery supplies roughly 50% of the left ventricle's mass. If the LV weighs about 200 g, how much myocardium depends on the LAD?

Myocardium supplied = 50% × 200 g
Myocardium supplied = 100 g
This is why LAD occlusion is nicknamed the 'widow-maker' — it can knock out half the LV's pumping muscle.

A patient has a heart rate of 75 bpm, and diastole occupies about two-thirds of each cardiac cycle (coronary flow happens mainly in diastole). How long is diastole per beat?

Cycle length = 60 s / 75 beats = 0.8 s per beat
Diastole ≈ (2/3) × 0.8 s ≈ 0.53 s
At faster heart rates, diastole shortens more than systole, which is why very high heart rates can reduce coronary perfusion time.

Flashcards

Quick quiz

Q1.Which vessels branch first off the aorta?

Correct answer: B. The left and right coronary arteries are the first branches off the aorta, just above the aortic valve.

Q2.Where does the coronary sinus drain?

Correct answer: B. The coronary sinus collects venous blood from the heart and empties it into the right atrium.

Q3.During which phase of the cardiac cycle does most coronary perfusion occur?

Correct answer: B. During diastole the myocardium relaxes, allowing coronary arteries to fill without being compressed.

Q4.The left anterior descending artery mainly supplies which region?

Correct answer: B. The LAD runs down the front of the heart, supplying the anterior wall and much of the interventricular septum.

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Common mistakes

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Assuming the heart gets its oxygen straight from the blood passing through its chambers. — Correct: The heart wall is too thick for diffusion alone — it needs its own dedicated coronary artery supply.

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Thinking coronary flow peaks during systole, like flow to other organs. — Correct: Coronary flow is highest during diastole, because a contracting myocardium squeezes its own vessels shut.

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Believing all people have identical coronary artery dominance. — Correct: Most people are right-dominant (RCA supplies the inferior wall/AV node), but left-dominant and co-dominant patterns also occur.

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Confusing coronary arteries with cardiac veins as the same vessels. — Correct: Coronary arteries deliver oxygenated blood to the myocardium; separate cardiac veins drain deoxygenated blood into the coronary sinus.

FAQ

What is coronary circulation?

Coronary circulation is the dedicated network of arteries and veins that supplies blood to the heart muscle itself, starting at the aortic root and draining into the right atrium via the coronary sinus.

What is an example of coronary circulation in action?

When the LAD artery narrows from plaque, the anterior wall of the left ventricle gets less oxygen, which can trigger angina or a heart attack — a direct example of coronary circulation at work.

How is coronary blood flow calculated?

Coronary flow can be estimated as a percentage of total cardiac output — at rest it's roughly 5%, rising several-fold during exercise as the heart demands more oxygen.

Why does coronary circulation matter clinically?

Blockage of coronary arteries (coronary artery disease) starves heart muscle of oxygen, causing angina, heart attacks, and is the leading cause of death worldwide.