False-colour angiogram (X-ray image) of the human heart, showing a mechanical Starr-Edwards aortic heart valve. A normal aortic valve regulates the flow of blood from the left ventricle into the aorta, the body's main artery, for distribution around the circulation. The valve consists of three cusps, shaped like half-moons. Malfunctions of the valve include fusion of the cusps, often the result of the scarring that follows rheumatic fever. This results in a narrowing of the valve's opening (aortic stenosis) with a consequent reduction in blood flow. An incompetent aortic valve may also cause blood to reflux back into the left ventricle (aortic regurgitation).