Aortic valve stenosis (also known as aortic stenosis) is a narrowing of the heart's aortic valve. Stenosis occurs when the valve leaflets thicken, stiffen or fuse, due to cholesterol and calcium deposits in the valve. This causes the valve opening to narrow. Consequently, the aortic valve is unable to open properly, blocking blood flow from the heart into the aorta and onwards to the rest of the body.

An obstruction of the aortic valve will cause the heart to work harder in pumping blood to the body. As a result, the amount of blood which is pumped is limited, and the extra work burden weakens the heart muscle.