Oxygen will go in our lungs when we inhale. blood will carry the oxygen through our heart. first, it will go to the left atrium. then in the left ventricle. it will pass the arteries and gas exchages in the capillaris. now, blood carries carbon dioxies. it will pass the veins and back to the heart. it pass through the right ventricle and right atrium, then it will go out in our lungs. carbon dioxide is being released.