Anatomy I · Topic 1 of 4
The heart: chambers, valves & vessels
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The heart is a four-chambered muscular pump lying in the middle mediastinum, enclosed in the pericardium. About two-thirds of its mass lies to the left of the midline. Understanding its orientation — rotated so the right ventricle faces anteriorly — is the key to reading ECGs, imaging and auscultation findings.
Orientation and surfaces
The apex points inferiorly, anteriorly and to the left, usually at the left 5th intercostal space in the midclavicular line. The base (posterior surface) is formed mainly by the left atrium.
The sternocostal (anterior) surface is mostly right ventricle; the diaphragmatic (inferior) surface is mostly left ventricle; the left (pulmonary) surface is mostly left ventricle.
The chambers
The right atrium receives the SVC, IVC and coronary sinus. Its smooth part (sinus venarum) is separated from the rough, pectinate-muscle part by the crista terminalis. The fossa ovalis is the remnant of the foramen ovale.
The right ventricle has trabeculae carneae, three papillary muscles and the septomarginal trabecula (moderator band), which carries the right bundle branch.
The left ventricle has walls roughly three times thicker than the right, two papillary muscles, and an outflow tract (aortic vestibule) leading to the aortic valve.
Valves and auscultation
Atrioventricular valves (tricuspid, mitral) are anchored by chordae tendineae to papillary muscles. Semilunar valves (pulmonary, aortic) have three cusps each and no chordae.
- Aortic — right 2nd intercostal space, parasternal
- Pulmonary — left 2nd intercostal space, parasternal
- Tricuspid — left 4th/5th intercostal space, lower sternal border
- Mitral — left 5th intercostal space, midclavicular line (apex)
Coronary circulation
The right coronary artery arises from the right aortic sinus and usually supplies the SA node (~60%) and the AV node (~80%). The left main coronary artery divides into the left anterior descending (LAD) and circumflex arteries.
Dominance is defined by which artery gives rise to the posterior descending artery — right-dominant in roughly 70% of people.
High-yield points
- The LAD is the most commonly occluded coronary artery.
- The left atrium is the most posterior chamber — it can compress the oesophagus when enlarged.
- The moderator band carries the right bundle branch.
- Heart sounds are best heard downstream of the valve, not over it.