Aortic valve stenosis is a condition in which the aortic valve is deformed and narrowed. The narrowing or stenosis is caused by valve leaflets that are thickened and fused. This prevents the valve from opening completely during systole. Systole is the phase of the heartbeat in which the ventricles contract. As a result, blood cannot flow easily into the aorta and pressure builds in the left ventricle. This can damage the heart muscle eventually. To open the valve and improve blood flow, a catheter procedure may be performed. A balloon catheter is inserted into the aorta and threaded through the narrow valve. The balloon on the catheter is then inflated. The aortic valve opening is widened by the inflated balloon. The catheter is removed and blood flows normally through the valve. There is often some degree of backward leakage through the valve, and most patients will require later intervention.