Valves help keep blood flowing in the proper direction. The human heart is basically two pumps in one--the right side contains deoxygenated blood and the left side contains oxygenated blood and each side is responsible for pumping the blood along specific pathways.
The aortic valve is located between the left ventricle of the heart and the aorta, the largest artery in the body. The purpose of the left side of the heart is to pump oxygenated blood to the aorta, so that this major artery can transport oxygen-rich blood to all parts of the body via systemic circulation. As the left ventricle contracts, oxygenated blood is pumped through the aortic valve. It has three flaps and blood flows through the valve into the aorta. The importance is that, as long as this valve functions properly, blood flows in the correct direction--out of the heart.
The term pulmonary refers to lungs, and it is the pulmonary valve that is responsible for allowing deoxygenated blood to be pumped from the right ventricle to the lungs to gain oxygen. The importance is that, as long as this valve is free of disease or defects, blood will be able to follow the pulmonary circulation pathway in the correct direction to allow blood to become oxygenated.