Anatomy of the Aortic Valve
The aortic valve has three parts, called "leaflets," that open and close. It functions as a one-way valve: when the left ventricle contracts, the valve only allows blood to flow out of the left ventricle and into the aorta. When the heart relaxes between contractions, the aortic valve closes, preventing blood in the aorta from returning to the left ventricle.
If calcium deposits build up on the aortic valve, the valve becomes hardened (calcified) over time. When this occurs, the leaflets do not open normally and the volume of blood ejected from the left ventricle is reduced. The heart's ability to supply the body with blood decreases, and blood backs up into the lungs.
The left ventricle initially compensates for increased resistance caused by aortic stenosis by thickening (i.e., increasing muscle mass) to help eject blood through the stenotic aortic valve into the aorta.
This helps overcome aortic stenosis at first, but the left ventricle progressively increases in diameter (dilates), stiffens, and gradually loses its ability to generate enough contractile force to compensate for the stenotic aortic valve. If aortic stenosis remains untreated, the left ventricle becomes further dilated and less able to contract and expel blood into the aorta.