Topography of the heart
The heart is located in the mediastinum (mediastinum), the central part of the thoracic cavity, between the right and left lungs. Based on adjacent anatomical structures, several surfaces of the heart are distinguished:
- Pulmonary surface (facies pulmonalis) — adjacent to the lungs on both sides;
- Sternocostal surface (facies sternocostalis) — faces anteriorly toward the sternum and ribs;
- Diaphragmatic surface (facies diaphragmatica) — inferior, adjacent to the diaphragm.
The heart has an apex (apex cordis) and a base (basis cordis). The apex projects onto the anterior chest wall in the area of the fifth intercostal space on the left, which is an important clinical landmark for palpating the apex beat.
Heart chambers and septa
The human heart has four chambers: two atria (atrium dextrum et sinistrum) and two ventricles (ventriculus dexter et sinister). They are separated by septa:
- Interventricular septum (septum interventriculare) consists of two parts: the upper fibrous (membranous) part (pars membranacea) and the lower muscular part (pars muscularis);
- The interatrial septum (septum interatriale) contains the oval fossa (fossa ovalis), which is a remnant of the fetal foramen ovale. Its margin is bounded by the limbus (limbus fossae ovalis), which is a remnant of the fibrous ring.
Right atrium and right ventricle
The superior and inferior venae cavae (vena cava superior et inferior) empty into the right atrium. The internal surface of the right atrial auricle features pectinate muscles (musculi pectinati). The roof of the right atrium contains the sinoatrial node, the cardiac pacemaker and an element of the conduction system.
Between the right atrium and the right ventricle lies the tricuspid valve (valva tricuspidalis). The right ventricle contains papillary muscles (musculi papillares) — anterior, posterior, and septal — from which chordae tendineae extend to the valve cusps. They prevent the cusps from everting during systole. From the right ventricle, blood enters the pulmonary trunk through the pulmonary valve with right, left, and anterior cusps.
Left atrium and left ventricle
The pulmonary veins (venae pulmonales) empty into the left atrium, carrying oxygenated blood from the pulmonary circulation. The wall of the left atrium is smoother, as it lacks major elements of the conduction system.
Between the left atrium and the left ventricle lies the bicuspid, or mitral, valve (valva mitralis). The name comes from its resemblance to a mitre, a bishop's head covering. The left ventricle also contains papillary muscles and chordae tendineae. At the aortic outlet lies the aortic valve, which is semilunar and tricuspid. The aortic bulb (bulbus aortae) gives rise to the right and left coronary arteries (arteriae coronariae) above the cusps, supplying the myocardium.
Fibrous skeleton of the heart
The heart has a fibrous skeleton, a framework to which myocardial muscle fibers and valve cusps attach. The heart has no bony framework, as continuous contractions require an elastic structure. The skeleton includes:
- Right fibrous ring — around the tricuspid valve;
- Left fibrous ring — around the mitral valve;
- Aortic fibrous ring;
- Pulmonary trunk fibrous ring;
- Right and left fibrous trigones (trigonum fibrosum dextrum et sinistrum), connecting the rings to each other.
Valve auscultation points
The anatomical projection and the auscultation point of a valve do not always coincide, but orientation by intercostal spaces is mandatory for clinical examination:
- Mitral valve — 5th intercostal space on the left, in the area of the apex beat (at the midclavicular line);
- Tricuspid valve — base of the xiphoid process, at the right sternal border in the 4th–5th intercostal space;
- Aortic valve — 2nd intercostal space to the right of the sternum;
- Pulmonary valve — 2nd intercostal space to the left of the sternum.
Intercostal spaces are counted from top to bottom: the first is the space between the clavicle and the 1st rib (essentially above the 1st rib), followed by the space between the 1st and 2nd ribs, and so on.
Key points
- The heart is located in the mediastinum and has sternocostal, diaphragmatic, and pulmonary surfaces.
- The apex of the heart projects into the 5th intercostal space on the left.
- The interventricular septum consists of muscular and fibrous (membranous) parts.
- The fossa ovalis of the interatrial septum is a trace of the embryonic foramen ovale.
- The tricuspid and mitral valves are anchored by chordae tendineae and papillary muscles.
- The coronary arteries arise from the aortic bulb above the cusps of the aortic valve.
- The fibrous skeleton of the heart is formed by four rings and two trigones.
- Auscultation points: mitral — apex, tricuspid — base of the xiphoid process, aortic — 2nd intercostal space on the right, pulmonary — 2nd intercostal space on the left.