In stage number one, the atrium of the heart, and that includes the right atrium and the left atrium, are fully relaxed. And at this moment in time, they both receive blood from the rest of our body. So let's begin with the right pump that contains the right atrium. So our blood, that is deoxygenated returns from the upper portion of the body via the superior vena cava. And the de oxygenated blood comes from the lower portion of the body via the inferior vena cava. And these two blood systems basically connect and they empty out into the right atrium of our heart, which is this chamber here.