These are the atrium ventricular valves. And they must be open to actually accept that blood from the atrium and into that ventricle. But when contraction takes place, the right and left atrial ventricular valves number one and three are actually closed. But number two and four, the semilunar valves we have, the pulmonary and the aortic valve, these open up to basically allow the movement of our blood from our heart into the systemic and into the pulmonary circulatory system of our our body. So when one and three are open, two and four are closed. But when one and three are closed, two and four are open.