Heart valves
As discussed previously, the heart consists of 4 chambers, the left atrium, left ventricle, right atrium and right ventricle. The regulation of normal blood flow requires the presence of valves at the exit point of the chambers. These valves allow the forward flow of blood when open and prevent backward flow when closed.

The mitral valve lies between the left atrium and ventricle. It is a complicated structure which consists of 2 leaflets that open and close, the papillary muscles which regulate the motion of the leaflets as well as the chords which connect the leaflets to the muscles. The valve allows the flow of blood from the atrium to the ventricle, while it prevents flow back into the atrium while the ventricle is contracting. A very small degree of backward flow is considered normal.

The aortic valve lies at the exit of the left ventricle. it usually consists of three leaflets. It is open during contraction allowing blood flow towards the aorta, while it closes during relaxation preventing blood flow back into the heart.

The tricuspid valve separates the right atrium and ventricle. it consists of 3 leaflets and its role is similar to the mitral valve. A small degree of backward flow is also considered normal.

The pulmonary valve lies at the exit point of the right ventricle. its role is similar to the aortic valve while a degree of backward flow is also normal.

The main conditions that affect heart valves are stenosis (narrowing), regurgitation (backward flow) and endocarditis (valve infection). The commonest conditions which are usually more significant haemodynamically affect the left sided valves and will be discussed further at a later stage.
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