So the right atrium begins to fill with deoxygenated blood and at this moment in time, it is fully relaxed. Now, at the same exact moment in time, the oxygenated blood that is coming back from the left lung found in this section and the right lung, found in this section that blood is coming back via the right and the left pulmonary vein. So we have the right pulmonary vein which is shown in the back of this diagram, and this is the left pulmonary vein. And they both empty out our oxygen blood and begin to fill the left atrium of the heart. So this takes place at the same exact moment in time. So our two atria are fully relaxed and blood begins to fill these two atria, the only distance is here we have deoxynated blood, and here we have the oxygenated blood.