Prosthetic aortic heart valve. The normal aortic (semi-lunar) valve lies between the aorta (main artery of the body) and the left ventricle of the heart. It regulates the flow of blood from heart to body, to enable blood distribution around the general circulation. The aortic valve naturally consists of three cusps, shaped like half-moons. Malfunctions of this valve include fusion of the cusps, often due to scarring that follows rheu- matic fever. The valve's opening narrows (aortic stenosis), with a consequent reduction in blood flow. An incompetent aortic valve may also cause blood to reflux back into the heart (aortic regurgitation), prompting replacement surgery.