The Structure of the Heart

The first diagram (immediately below) is a cut-away section through the heart, showing its physical appearance and labelling its major components and blood vessels. The simpler diagrams below it are line drawings including essential information in a form that is easier to reproduce in exams.

Illustration of the Physical Form of the Heart

Diagram (1): Physical Appearance and Major Components of the Heart

The heart is a muscular cone-shaped organ about the size of a clenched fist of the same person. It is located in the upper body (chest area) between the lungs, and with its pointed end (called the apex) downwards, forwards, and pointing towards the left.

The main purpose of the heart is to pump blood around the body.

The basic structure of the heart as shown above can be described as follows:

The heart is divided into separate right and left sections by the interventricular septum, or just the 'septum' when the context is obvious. Each of these (right and left) sections is also divided into upper and lower compartments known as atria and ventricles,

The four main chambres of the heart are:

• Right Atrium ('RA' in the diagrams on this page)
• Right Ventricle ('RV' in the diagrams on this page)
• Left Atrium ('LA' in the diagrams on this page)
• Left Ventricle ('LV' in the diagrams on this page)

Deoxygenated blood (from the body) is pumped through the right atrium and the right ventricle (to the lungs), while oxygenated blood (from the lungs) is pumped through the left atrium and the left ventricle (to the body).

• Deoxygenated blood enters the right atrium from the superior vena cava and the inferior vena cava.
• Deoxygenated blood leaves the right ventricle by pulmonary artery, which takes blood to the lungs via the right and left brances of the pulmonary artery.
• Oxygenated blood enters the left atrium from the pulmonary veins.
  These may be labelled as 'right pulmonary veins' and 'left pulmonary veins'.
• Oxygenated blood leaves the left ventricle by ascending aorta, which takes blood to the body via its system of arteries, arterioles, and capillaries. Major arteries leading from the heart (via the ascending aorta) include the brachiocephalic artery, the left common carotid artery, and the left subclavian artery (illustrated above). These are just a few of the main arteries of the body.

It is essential that blood flows in the correct direction through the heart so the structure of the heart includes a series of valves.

• The tricuspid valve separates the right atrium from the right ventricle.
• The pulmonic / pulmonary valve separates the right ventricle from the pulmonary artery.
• The mitral (also known as the bicuspid) valve separates the left atrium from the left ventricle.
• The aortic valve separates the left ventricle from the ascending aorta.

Line Drawings of the Basic Structure of the Heart

Although Diagram (1) above is a clear illustration of the structure of the heart, it may be difficult to draw quickly in examinations. The following diagrams are less detailed and not as fully labelled (more labels could be added), but may be more convenient to sketch rapidly if required to do so.

Diagram 2(a) is a simplification of Diagram (1).

Diagram 2(b) includes additional information about structures concerned with the system of electrical conduction operating in the heart, which is described on the page about the functions of the heart.

Diagram 2(a)

Diagram 2(b)

More about the functioning of the heart and the vascular system generally are included on other pages in this section.