The left side of the heart pumps oxygen-rich blood into the aorta, which is the main artery in the body. Before the blood reaches the aorta, it collects in an area called the left ventricle. The left ventricle squeezes, or contracts, regularly. That sends blood through the aortic valve and into the aorta.
Aortic stenosis is a narrowing of the opening of the aortic valve.
This partly blocks blood flow from the left ventricle. The aortic valve lies between the left ventricle and the aorta. Normally the valve opens when the ventricle contracts so that oxygen-rich blood can be pumped into the aorta and out to the rest of the body. When aortic stenosis has occurred, the opening of the valve is narrower than normal. This reduces the amount of blood flow to the body.