AORTIC VALVE, a valve separating the left ventricle of the heart and the aorta. It consists of three semicircular, pocket like folds, whose free edges are directed away from the heart. Blood flows into the aorta with each beat of the heart, but be tween beats the blood is prevented from flowing backward by the valve leaflets. The pockets fill with an eddying current of blood and their free edges meet exactly. When this valve is affected by certain diseases, notably, rheumatic fever and syphilis, the deli cate leaflets become shrunken and thick and no longer perform their function. The valve leaks, thus imposing an extra burden on the heart which sometimes leads to symptoms of heart failure. The aortic valve is second only to the mitral in the frequency with which it becomes diseased.