Aortic valve stenosis means that the aortic valve, which allows blood to leave the heart, has narrowed and can't open all the way. The smaller opening causes high pressure in the left side of the heart (called the left ventricle), and the heart has to work harder to pump blood.
Over time, the extra work causes the walls of the left ventricle to thicken. A thick heart does not work well and is unable to pump the amount of blood your body needs. Patients feel shortness of breath, dizziness, and chest pain.