Now, the reason for that is because if we examine inside the lungs, inside the alveoli of the lungs, those alveoli are completely filled with the fluid. And so because of that, there will be a high resistance and a high pressure inside the lungs. And because of this high pressure in the lungs, and because the lungs are not functional inside that developing Fetus, this blood will move into the left atrium and not into the left ventricle. So because on the right side of the heart we have a higher pressure then on the left side of the heart, as a result of the high pressure inside the lungs, the majority of that blood, the partially oxygenated blood, will move from the right atrium, this chamber here, via the pharamino valley and into the left atrium of the heart. Now, what exactly is this for amino valley? Well, in that developing Fetus, the wall that is separating the two atria contains this one way door, a valve system.