Human Anatomy, Part 2 - K. A. Dubenko, A. K. Kolomiysev, Yu. B. Chaykovsky 2008

Special Section
Cardiovascular system, systema cardiovasculare — Special Section
Heart — Topography of the Heart

The Heart is located in the middle Mediastinum (mediastinum medium) within the pericardial sac, situated between the layers of the mediastinal Pleura. It lies asynchronously relative to the median plane of the body, with approximately two-thirds of its mass positioned to the left and one-third to the right. The longitudinal axis of the heart extends obliquely from the base to the apex, running downward, forward, and to the left. The anatomical position of the heart varies—it may be transverse, oblique, or vertical. A vertical orientation is more common in individuals with a narrow, elongated Thorax, whereas a transverse orientation typically occurs in those with a broad, short chest. In the living subject, the BOUNDARIES OF THE heart are determined via Percussion (percussio)* or by projecting the organ onto the anterior thoracic wall using radiography (Figs. 10 and 11).

The superior border of the heart corresponds to the upper margin of the third costal cartilages. The right border extends 2–3 cm to the right of the right sternal margin, reaching the 3rd to 4th Ribs, where it transitions into the inferior border at the level of the 5th rib. The inferior border courses obliquely downward and to the left, intersecting the Sternum just above the Base of the xiphoid process, extends to the left 6th intercostal space, crosses the Cartilage of the 6th rib, and reaches the 5th intercostal space 1.5–2 cm medial to the midclavicular line (linea medioclavicularis).

The left border extends from the cartilage of the 3rd rib down to the apex of the heart.

The apical heartbeat (apex beat) can be palpated in the fifth intercostal space along the left midclavicular line (linea mammillaris sinistra), about 1 cm medial to it. The orifices of the aorta and pulmonary trunk, along with their cusps, are projected at the level of the 3rd intercostal space; the semilunar cusps of the aortic valve lie posterior to the left half of the sternum, while those of the pulmonary trunk are located near its left margin. The atrioventricular orifices project along a line drawn from the attachment site of the 5th right costal cartilage to the attachment site of the 3rd left cartilage. The PROJECTION OF THE right atrioventricular orifice occupies the right half of this line, and the left orifice occupies the left half.

Auscultation (listening to the heart sounds) is performed at the following standard anatomical areas (Fig. 10):

The aortic valve sounds are best auscultated In the second right intercostal space near the sternal margin; the bicuspid (mitral) valve sounds, at the apex of the heart; and the tricuspid valve sounds, over the sternum on the right, opposite the 5th costal cartilage. The pulmonary valve sounds are heard in the second left intercostal space adjacent to the sternum.

* Percussion produces a dull sound due to the Physical Properties of the heart, specifically its thick muscular walls and the Blood contained within its chambers.