External structure and surfaces
The heart has an anteroposteriorly flattened, irregularly conical shape, which is not constant and depends on age, body constitution, and the presence of pathologies.
Spatially, the organ is oriented as follows:
- Base (basis) is directed superiorly, to the right, and posteriorly. Large vascular trunks forming the root of the heart are located in this area.
- Apex (apex) is directed anteriorly, inferiorly, and to the left.
Traditionally, three main surfaces are distinguished:
- Sternocostal (facies sternocostalis) — the anterior surface, which is largely formed by the wall of the right ventricle.
- Diaphragmatic (facies diaphragmatica) — the inferior surface adjacent to the diaphragm (formed predominantly by the left ventricle).
- Pulmonary (facies pulmonalis) — the lateral surface.
Sulci and vessels of the surfaces
The relief of the organ is determined by sulci containing nourishing vessels surrounded by subepicardial adipose tissue.
- Coronary sulcus (sulcus coronarius) runs transversely and separates the atria from the ventricles. On the inferior surface, it lodges the circumflex branch of the left coronary artery, the coronary sinus, the small cardiac vein, and the right coronary artery.
- Anterior interventricular sulcus (sulcus interventricularis anterior) corresponds to the interventricular septum and divides the anterior wall into a larger right portion (right ventricle) and a smaller left portion. It contains the matching branch of the left coronary artery and the great cardiac vein.
- Posterior interventricular sulcus runs along the posterior margin of the septum. It lodges the posterior interventricular branch of the right artery and the middle vein.
The initial segments of the great vessels at the base lie in a strict order: superior and posterior is the superior vena cava, to the left and anterior is the ascending aorta, and further to the left is the pulmonary trunk.
Skeletotopy: borders of the heart
Knowledge of the projection of borders onto the anterior thoracic wall is a basic requirement for physical examination.
- Right border: formed by the superior vena cava and the margin of the right atrium. Runs from the upper edge of the right 2nd rib cartilage to the 3rd rib (stepping back 1.0–1.5 cm from the sternum), then descends in an arch to the 5th rib.
- Inferior border: formed by the margins of both ventricles. From the 5th rib on the right, the line descends obliquely to the left, crossing the sternum above the base of the xiphoid process, and heads toward the fifth intercostal space on the left.
- Left border: a complex contour (aortic arch, pulmonary trunk, left auricle, and left ventricle). Extends downward from the lower edge of the left 1st rib. At the level of the 2nd intercostal space is the trunk, at the level of the 3rd rib is the auricle. Further, the line runs in a convex arch to the apex in the 5th intercostal space.
Projection of orifices and valves
The projection of the valvular apparatus also has clear skeletotopic landmarks:
- Right atrioventricular orifice (tricuspid valve) — projected onto the right half of the sternum along a line connecting the end of the right 5th rib with the outer end of the left 1st rib cartilage.
- Left atrioventricular orifice (bicuspid/mitral valve) — located at the left sternal margin at the level of the 3rd intercostal space.
- Aortic orifice (semilunar valves) — located behind the left sternal margin at the level of the 3rd intercostal space.
- Pulmonary trunk orifice — lies slightly to the left of the aortic orifice, at the left sternal margin at the level of the 3rd rib cartilage.
Syntopy (relations with organs)
The heart is located in the mediastinum and isolated by the pericardium.
- Anteriorly, the area of the right ventricle partially abuts the sternum and the cartilages of the left 3rd–5th ribs. However, the main part is hidden by the costomediastinal pleural recesses and the margins of the lungs.
- Pulmonary and posterior-inferior surfaces are in contact with the mediastinal pleura and lungs.
- Posterior wall of the left atrium has crucial topographical relations: it abuts the left main bronchus, esophagus, aorta, and vagus nerves.
- Posterior wall of the right atrium is located anteriorly and inferiorly to the right main bronchus.
Briefly: answers to topical questions
What branches does the left coronary artery give off?
The left coronary artery gives off several major branches arising from its main trunk.
- Anterior interventricular branch (r. interventricularis anterior) — runs in the sulcus of the same name, giving off septal and diagonal branches.
- Circumflex branch (r. circumflexus a. coronariae sinistrae) — runs in the left coronary sulcus, giving off branches of the obtuse margin.
- Intermediate artery — present in about a third of the population, runs along the wall of the left ventricle between the anterior descending and circumflex branches.
What nodes and bundles make up the cardiac conduction system?
The cardiac conduction system includes specialized nodes, bundles, and fibers.
- Sinoatrial node (nodus sinuatrialis) — coordinates automatism and acts as the pacemaker.
- Atrioventricular node — participates in impulse conduction.
- Bundle of His — located in the upper part of the interventricular septum, divides into bundle branches and their ramifying fibers.
- Purkinje fibers — form a network in the ventricular myocardium.
Where on the anterior chest wall are the auscultation points of the heart valves located?
The points of best auscultation of the heart valves on the anterior chest wall correspond to the sites of heart sound generation.
- Mitral valve — auscultated at the apex of the heart (in the 5th intercostal space).
- Tricuspid valve — auscultated at the base of the xiphoid process (at the lower sternal margin).
- Aortic valve — auscultated in the 2nd intercostal space to the right of the sternum.
- Pulmonary valve — auscultated in the 2nd intercostal space to the left of the sternum.
Which nerves and plexuses innervate the heart?
Cardiac innervation is associated with branches of the sympathetic trunks, vagus, and phrenic nerves, which form cardiac and cardiopulmonary plexuses.
- Sympathetic trunk (truncus sympathicus) — its superior cervical ganglion gives rise to the superior cervical cardiac nerve (n. cardiacus cervicalis superior).
- Vagus nerve (n. vagus) and sympathetic trunks participate in the formation of cardiopulmonary plexuses.
- Cardiac plexus (plexus cardiacus) is located in the mediastinal adipose tissue.
- Cardiopulmonary plexuses — superficial left and deep right; their branches head toward the heart and pericardium.
Relative positions of the vessels at the base of the heart (from right to left): Vein (superior vena cava) → Aorta → Trunk (pulmonary) — mnemonic device "VAT".
Class and exam questions
Which heart chamber forms the major part of its anterior surface?
The anterior (sternocostal) surface of the heart is formed predominantly by the anterior wall of the right ventricle.
What forms the apex of the heart, and where is it projected?
The apex is formed by the left ventricle. Its projection onto the chest wall is located in the fifth intercostal space on the left, 1.5–2.0 cm medial to the left midclavicular line.
Where does the coronary sulcus run, and what does it contain?
It runs transversely, separating the atria and ventricles. It contains the right coronary artery, the circumflex branch of the left artery, the coronary sinus, and the small cardiac vein.
Which structures are in contact with the posterior wall of the left atrium?
It is bordered by the left main bronchus, esophagus, descending aorta, and vagus nerve trunks.
What else to study on this topic
- Topography of the elements of the posterior wall of the pericardial cavity (sinuses and folds)
- Detailed course of the branches of the left and right coronary arteries
- Formation of venous drainage and the coronary sinus basin
- Nervous apparatus of the heart: vagus nerves and cardiac plexus
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