And that moves the deoxynative blood and begins to fill the right ventricle of the right pump of our heart. So at this moment in time, the right atrium is contracting, but the right ventricle, which begins to fill, is fully relaxed. Now, this also means, because our right ventricle is being filled, we don't want the backflow of blood from these blood vessels, which are basically the pulmonary arteries, back into the right ventricle. And that's exactly why the pulmonary semi lunar valve, this valve right here, is closed so that we have a one way movement, a unidirectional movement of blood this way from the right atrium to the right ventricle. Now, at the same exact moment in time, this is what begins to take place at the left side of our heart in the left pump. So just as the right atrium is fully filled, the left atrium is also fully filled, but it's filled with oxygenated blood.