Aortic Valve :One of the four one-way valves that keep blood moving properly through the various chambers of the heart. The aortic valve, also called a semi-lunar valve, separates the left ventricle from the aorta. As the ventricles contract, it opens to allow the oxygenated blood collected in the left ventricle to flow throughout the body. It closes as the ventricles relax, preventing blood from returning to the heart. Valves on the heart’s left side need to withstand much higher pressures than those on the right side. Sometimes they can wear out and leak or become thick and stiff.