Now, once the blood fills the right atrium, it then moves into the right ventricle and it's the right ventricle that is responsible for creating that contraction and moving that deoxynated blood into the pulmonary circulation of the cardiovascular system into these pulmonary arteries that extend into the left lung and into the right lung. So we have the left lung here and we have the right lung here. Now, once our blood is inside the lung, it is oxygenated and then it moves into our left atrium via the pulmonary vein. So this is the left atrium. The left atrium, once it fills with blood, it moves into the left ventricle. And it's the left ventricle that is the thickest of all these chambers.