And when they contract, they open up the tricuspid valve and they also open up our bicuspid, or mitral valve. So let's begin with the right pump. So the right atrium is fully filled with the deoxynative blood and it contracts and enforces the opening of our tricuspid valve. 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.