So when our left ventricle is relaxed, blood flows from the left atrium into the left ventricle. And to make sure this blood flows, this valve number three must be open. But when our left ventricle contracts, valve number three closes to prevent the backflow, the movement of blood back into the left atrium. Now what about valve number four? This is known as the aortic valve or the aortic semi lunar valve. This is the valve that connects the left ventricle to our aorter and our systemic circulation.