The heart has four valves - one for each chamber of the heart. The valves keep blood moving through the heart in the right direction.
The mitral valve and tricuspid valve are located between the atria (upper heart chambers) and the ventricles (lower heart chambers).
The aortic valve and pulmonic valve are located between the ventricles and the major blood vessels leaving the heart.
The valves are made of strong, thin flaps of tissue called leaflets or cusps.
The leaflets open to let blood move forward through the heart during half of the heartbeat. They close to keep blood from flowing backward during the other half of the heartbeat.
The mitral valve has only two leaflets; the aortic, pulmonic and tricuspid valves 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 valves are also supported by:
- Chordae tendineae: tough, fibrous strings. These are similar to the strings supporting a parachute.
- Papillary muscles: part of the inside walls of the ventricles.
The chordae tendineae and papillary muscles keep the leaflets stable to prevent blood from flowing backward.
How Valves Work
The four valves are to open and close to let blood flow through the heart. The steps below show how the blood flows through the heart and describes how each valve works to keep blood moving.
1. Open tricuspid and mitral valves
Blood flows from the right atrium into the right ventricle through the open tricuspid valve, and from the left atrium into the left ventricle through the open mitral valve.
2. Closed tricuspid and mitral valves
When the right ventricle is full, the tricuspid valve closes and keeps blood from flowing backward into the right atrium when the ventricle contracts (squeezes).
When the left ventricle is full, the mitral valve closes and keeps blood from flowing backward into the left atrium when the ventricle contracts.
3. Open pulmonic and aortic valve
As the right ventricle begins to contract, the pulmonic valve is forced open. Blood is pumped out of the right ventricle through the pulmonic valve into the pulmonary artery to the lungs.
As the left ventricle begins to contract, the aortic valve is forced open. Blood is pumped out of the left ventricle through the aortic valve into the aorta. The aorta branches into many arteries and provides blood to the body.
4. Closed pulmonic and aortic valves
When the right ventricle finishes contracting and starts to relax, the pulmonic valve snaps shut. This keeps blood from flowing back into the right ventricle.
When the left ventricle finishes contracting and begins to relax, the aortic valve snaps shut. This keeps blood from flowing back into the left ventricle.
This pattern is repeated, causing blood to flow continuously to the heart, lungs, and body. The four normally working heart valves make sure blood always flows freely in one direction and that there is no backward leakage.