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There are two different types of valves in the heart, atrioventricular (AV) and semilunar (SV). The atrioventricular valves are the mitral and tricuspid valves, which regulate the blood flow from the left and right atriums to the left and right ventricles. The semilunar valves are the aortic valve and the pulmonic valve, which allow the blood to flow from the left ventricle to the aorta and from the right ventricle to the pulmonary artery.
The semilunar valves work using pressure. As the heart beats, it creates blood pressure in the circulatory system. This pressure can also be affected by hormones released in the body, which cause the muscles around the vessels to contract and restrict blood flow. The aortic semilunar valve works by sensing pressure in the left ventricle. When the pressure in the ventricle becomes greater than the pressure in the aorta, the valve opens, allowing blood flow to go through the valve and into the aorta, then pumped through the rest of the system. When the heart beats, the pressure change causes the valve to close, disallowing any blood to backflow into the heart. The same process occurs in the pulmonic valve, only the pressure changes between the right ventricle and the pulmonary artery.
Certain conditions and health issues may lead to problems with the semilunar heart valve. One of the most common problems is aortic insufficiency, which is when a leaking valve allows blood to backflow into the heart. The semilunar valve may also block blood flow through the valve by not opening fully, called aortic valve stenosis. Valve malfunction may also be congenital, such as being born with a bicuspid aortic valve. A bicuspid aortic valve has only two connection cusps, verses a healthy aortic valve, which has three. In most of these circumstance, the valve itself will eventually need to be replaced.
Damage to the semilunar valves can cause dangerous problems, causing blood to backflow into the heart. However, modern medicine has created artificial heart valves that can be made up of both synthetic or organic materials. These devices can be implanted into the heart via open heart surgery. Synthetic valves will usually outlast their host. However, organic hearts tend to wear down and may need to be replaced at some point in a patient's life, depending on how late in life they were installed.