Aortic stenosis is a narrowing of the aortic valve. The aortic valve controls the blood flow between the heart's main pumping chamber and main artery (aorta).
Aortic stenosis occurs when the aortic valve becomes narrow and blocks the flow of blood from the heart to rest of the body. When the aortic valve gets very narrow, the heart must work harder to pump blood around the body.
As a result, the heart muscle gets thicker, stiffer and, over time, weaker. This weakness of the heart muscle is called heart failure.