The heart muscle gets its own blood supply from the coronary arteries, which branch off the aorta just above the aortic valve. They fill mainly during diastole, when the heart muscle relaxes.
Left main and its branches
The left main coronary artery splits into the left anterior descending (LAD) and the circumflex. The LAD feeds the front wall and most of the septum; the circumflex feeds the lateral wall.
Right coronary artery
The right coronary artery (RCA) feeds the right ventricle and, in most people, the inferior wall. It usually supplies the sinus and AV nodes too, so an inferior heart attack can cause slow rhythms and heart block.
Narrowing and blockage
Plaque narrows an artery slowly and causes chest pain with exertion (angina). When a plaque ruptures and a clot forms on it, flow stops and the muscle starts to die within minutes.
| Artery | Wall supplied | ECG leads |
|---|---|---|
| LAD | Anterior wall and septum | V1 to V4 |
| Circumflex | Lateral wall | I, aVL, V5, V6 |
| RCA | Inferior wall and right ventricle | II, III, aVF |
At the bedside
ST elevation in a group of related leads points to the blocked artery. In an inferior STEMI, check right-sided leads before nitroglycerin, because right ventricle involvement makes blood pressure drop easily.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).