Anatomy chapters
Anatomy of the heart
The surfaces, chambers and valves of the heart, the coronary arteries and veins, the conducting system and the pericardium, with the clinical points examiners link to them.
- The right ventricle forms most of the anterior surface; the left ventricle forms the apex; the left atrium forms most of the base.
- The RCA usually supplies the SA and AV nodes; the LAD supplies the front of the interventricular septum and is the commonest site of blockage.
- Pericardium: the transverse sinus is where a clamp is passed behind the aorta and pulmonary trunk in heart surgery.
On this page
Overview
The heart is a muscular pump with four chambers, lying in the middle mediastinum inside the pericardium.
The right side pumps blood to the lungs. The left side pumps blood to the body. Valves keep flow in one direction, and a conducting system sets the rhythm.
Position, surfaces and borders
The heart lies obliquely, with about a third to the right of the midline and two thirds to the left.
- Apex: formed by the left ventricle. It lies in the left fifth intercostal space, about 9 cm from the midline (the midclavicular line). The apex beat is felt here.
- Base (posterior surface): formed mainly by the left atrium.
- Anterior (sternocostal) surface: mainly the right ventricle.
- Inferior (diaphragmatic) surface: mainly the left ventricle, with part of the right.
| Border | Formed by |
|---|---|
| Right | Right atrium |
| Left | Left ventricle (and the left auricle) |
| Inferior | Right ventricle (and a little of the left at the apex) |
The left atrium lies directly in front of the oesophagus. An enlarged left atrium (mitral stenosis) can press on it and cause difficulty swallowing; this relation is also used in transoesophageal echocardiography.
Chambers
Right atrium
Receives the superior and inferior venae cavae and the coronary sinus.
- The smooth part (sinus venarum) and the rough part (with musculi pectinati) are separated by the crista terminalis.
- The fossa ovalis on the septum is the remnant of the fetal foramen ovale.
Right ventricle
- Its wall has muscular ridges, the trabeculae carneae.
- Papillary muscles hold the cusps of the tricuspid valve through chordae tendineae.
- The moderator band (septomarginal trabecula) crosses from the septum to the anterior papillary muscle and carries the right bundle branch.
- The smooth outflow part, the infundibulum, leads to the pulmonary trunk.
Left atrium
Receives the four pulmonary veins. It is mostly smooth-walled.
Left ventricle
Its wall is about three times thicker than the right, because it pumps to the whole body. Two papillary muscles hold the mitral valve cusps.
Valves
| Valve | Position | Cusps | Best heard (auscultation area) |
|---|---|---|---|
| Tricuspid | Right atrium to right ventricle | 3 | Lower left sternal edge |
| Pulmonary | Right ventricle to pulmonary trunk | 3 (semilunar) | Left 2nd intercostal space, next to the sternum |
| Mitral (bicuspid) | Left atrium to left ventricle | 2 | Apex (left 5th space, midclavicular line) |
| Aortic | Left ventricle to aorta | 3 (semilunar) | Right 2nd intercostal space, next to the sternum |
Valve sounds are not heard best over the valves themselves, but where blood flow carries the sound towards the chest wall.
The coronary arteries arise from the aortic sinuses: the right coronary from the anterior (right) sinus and the left coronary from the left posterior sinus.
Coronary arteries
Right coronary artery (RCA)
Runs in the right atrioventricular groove. Branches include:
- SA nodal artery (in about 60% of people).
- Right marginal artery.
- AV nodal artery (in most people).
- Posterior interventricular (descending) artery in most people.
Left coronary artery
A short trunk that divides into:
- Anterior interventricular artery (left anterior descending, LAD): supplies the front of both ventricles and the anterior two thirds of the septum.
- Circumflex artery: runs in the left atrioventricular groove and gives the left marginal artery.
The LAD is the artery most often blocked. It supplies the front of the left ventricle and most of the septum.
Dominance
The artery that gives the posterior interventricular artery is called "dominant". In most people, this is the RCA (right dominance).
Dominance is defined by the origin of the posterior interventricular artery, not by which artery is bigger.
Veins of the heart
Most cardiac veins drain into the coronary sinus, which lies in the posterior atrioventricular groove and opens into the right atrium.
- Great cardiac vein: runs with the LAD.
- Middle cardiac vein: runs with the posterior interventricular artery.
- Small cardiac vein: runs with the right marginal artery.
Small anterior cardiac veins and the smallest (Thebesian) veins open directly into the chambers.
Conducting system
- SA node: the pacemaker, in the wall of the right atrium at the upper end of the crista terminalis, near the opening of the superior vena cava.
- AV node: in the atrial septum, near the opening of the coronary sinus. It delays the impulse so the atria empty before the ventricles contract.
- Bundle of His: the only normal electrical link between atria and ventricles; it divides into right and left bundle branches in the septum.
- Purkinje fibres: spread the impulse through the ventricular walls.
Pericardium
- Fibrous pericardium: a tough outer sac, attached to the central tendon of the diaphragm. It stops the heart over-filling.
- Serous pericardium: a parietal layer lining the fibrous sac and a visceral layer (epicardium) on the heart, with a thin film of fluid between.
Two sinuses lie in the pericardial cavity:
- Transverse sinus: behind the aorta and pulmonary trunk and in front of the superior vena cava. Surgeons pass a finger or clamp through it in heart surgery.
- Oblique sinus: a blind pocket behind the left atrium.
The fibrous and parietal pericardium are supplied by the phrenic nerves and are sensitive to pain. The visceral layer is not.
Clinical relevance
Angina and myocardial infarction
How it happens: narrowing or blockage of a coronary artery.
What you see: central chest pain that may spread to the left arm, neck and jaw. Pain fibres from the heart enter the spinal cord at T1 to T4, the same segments that supply the skin of the inner arm, so the pain is referred there.
Cardiac tamponade
How it happens: blood or fluid collects in the pericardial cavity, for example after a stab wound.
What you see: the heart cannot fill. Low blood pressure, raised neck veins and muffled heart sounds. The fluid is drained by a needle passed from below the xiphoid process.
Pericarditis
How it happens: inflammation of the pericardium.
What you see: sharp chest pain, worse lying flat, sometimes felt at the shoulder tip because of the phrenic nerve. A friction rub may be heard.
Common angles: which chamber forms each border and surface, the left atrium's relation to the oesophagus, the blood supply of the SA and AV nodes, coronary dominance, the artery most often blocked, the transverse sinus, the moderator band and referred cardiac pain.
Quick revision
- Apex: left ventricle, left 5th intercostal space, midclavicular line.
- Anterior surface: right ventricle. Base: left atrium (in front of the oesophagus).
- Right border: right atrium. Left border: left ventricle.
- RCA: SA node (about 60%), AV node, and usually the posterior interventricular artery.
- LAD: anterior two thirds of the septum; commonest blockage.
- Coronary sinus opens into the right atrium.
- Transverse sinus: behind the aorta and pulmonary trunk.
Written by The House Job from standard anatomy references (Snell's Clinical Anatomy by Regions is the book named in the UHS PGET syllabus).
FAQ
Which artery usually supplies the SA node?
The right coronary artery, in about 60% of people.
What is coronary dominance?
It refers to which artery gives the posterior interventricular artery. In most people this is the right coronary artery.
What forms the base of the heart?
Mainly the left atrium, with a small part of the right atrium.
Why is heart pain felt in the left arm?
Pain fibres from the heart enter the same spinal segments (T1 to T4) as nerves from the skin of the inner arm.