The function of the two semilunar valves of the heart, the aortic valve and the pulmonary valve, is to allow blood to be forced into the arteries from the ventricles and to prevent blood from flowing back from the arteries into the ventricles. The closure of these two valves creates the second heart sound of a heartbeat.
The aortic valve is between the left ventricle and the aorta. The pulmonary, or pulmonic, valve is between the right ventricle and the pulmonary artery. Each valve normally has three cusps. They are called semilunar valves because they are shaped like half-moons.
Dysfunction of the aortic or pulmonary valve can lead to various types of heart disease. For instance, stenosis is a condition that prevents the aortic or pulmonary valve from opening properly, making the heart pump harder and creating a buildup of pressure. This can be caused by a congenital heart defect, aging or rheumatic fever. Exercise can exacerbate symptoms such as chest pressure or pain, dizziness, tiredness, shortness of breath or racing heart. Once symptoms of stenosis become apparent, surgery is usually necessary. Another valvular heart disease is regurgitation, also known as insufficiency, a condition in which a semilunar valve does not function properly, and blood flows in the wrong direction. Aortic or pulmonary insufficiency can be treated either medically or surgically.