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. So when the left ventricle is relaxed, it accepts that blood from this left atrium. So valve number three is open, but valve number four, the aortic valve, is closed. But when contraction of the left ventricle takes place, number three closes.