The aortic valve is one of the four valves that control the direction of blood flow through the heart. Specifically, it plays a vital role in controlling blood flow between the left ventricle and the aorta. Failure of the aortic valve to open or close completely can have serious and life-threatening consequences and requires surgical intervention to correct.
The aortic valve, along with the pulmonary valve, is one of the semilunar valves of the heart. It is located posterior to the pulmonary valve at the origin of the aorta between the aorta and the left ventricle. The aortic valve is a thin disk — less than 1mm thick — of dense irregular fibrous connective tissue covered with endothelium. It is divided into three segments known as cusps or leaflets. Each cusp is triangular and named for its position within the valve: right, left, and posterior. The cusps separate to allow blood to enter the aorta and join together tightly to prevent blood in the aorta from reentering the heart. When viewed in cross-section, it becomes apparent that the cusps are curved in a crescent moon shape that provides the aortic valve with its classification as a semilunar valve. The cusps are open on the concave side of their crescent, allowing blood on the aortic side to fill the cusps and close the valve.
Blood flow through the heart and blood vessels always moves from regions of higher pressure to regions of lower pressure. During ventricular systole, the left ventricle contracts and increases its pressure above the pressure within the aorta. Because of this change in pressure, the left ventricle pumps blood through the aortic valve and into the aorta. In response to the increased blood pressure, the cusps of the aortic valve separate and fold flat against the walls of the aorta.
At the end of ventricular systole, the left ventricle stops contracting, and the pressure within the ventricle decreases below the pressure inside the aorta. Blood in the aorta begins to move backward, or regurgitate, toward the left ventricle and fills the cup-like cusps of the aortic valve. As the cusps fill with blood, they expand like tiny parachutes and merge to block the regurgitation of blood.
There are two common disorders of the aortic valve: aortic valve stenosis and aortic valve insufficiency. Aortic valve stenosis is the narrowing or incomplete opening of the aortic valve due to scarring. Over the course of a lifetime, the aortic valve is under intense pressure that can damage the tissues of the valve. This damage leads to scarring and calcification that hardens the valve and makes it less flexible. Aortic valve insufficiency is a condition where the cusps of the aortic valve do not meet fully and fail to close the valve completely. This failure to close leads to regurgitation of blood back to the left ventricle. In both cases, aortic valve replacement surgery is required to restore proper function to the valve and the heart.