The heart is a four-chambered, hollow organ.

It is divided into the left and right side by a muscular wall called the septum. The right and left sides of the heart are further divided into:

  • two atria - top chambers, which receive blood from the veins and
  • two ventricles - bottom chambers, which pump blood into the arteries

The atria and ventricles work together, contracting and relaxing to pump blood out of the heart.

As blood leaves each chamber of the heart, it passes through a valve. There are four heart valves within the heart:

  • mitral valve
  • tricuspid valve
  • aortic valve
  • pulmonic valve (also called pulmonary valve)

Inside the heart

The tricuspid and mitral valves lie between the atria and ventricles. The aortic and pulmonic valves lie between the ventricles and the major blood vessels leaving the heart.

The heart valves work the same way as one-way valves in the plumbing of your home, preventing blood from flowing in the wrong direction.

Each valve has a set of flaps, called leaflets or cusps. The mitral valve has two leaflets; the others have three. The leaflets are attached to and supported by a ring of tough, fibrous tissue called the annulus. The annulus helps to maintain the proper shape of the valve.

The leaflets of the mitral and tricuspid valve are also supported by tough, fibrous strings called chordae tendineae. These are similar to the strings supporting a parachute. The chordae tendineae extend from the valve leaflets to small muscles, called papillary muscles, which are part of the inside walls of the ventricles

The normal aortic valve

The normal mitral valve

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