The Aortic valve is located at the outlet of the Aorta and delimits the Aorta from the left ventricle.
The Aortic valve enables passage of blood through it into the Aorta during systole, the phase of contraction of the left ventricle.
During diastole, when the ventricle is relaxed and the pressure in it decreases, there is risk of reverse blood flow from the Aorta (because the pressure therein is higher) into the left ventricle. The Aortic valve is here to prevent such back flow.
In instances when the valve is damaged or does not close properly, leakage into the left ventricle (regurgitation) can occur. Such leak reduces the amount of blood pumped into the Aorta on the one hand and constitutes an additional load for the left ventricle on the other hand .