The circulatory system ensures that the oxygen we inhale reaches the organs, and that carbon dioxide is exhaled as we breathe. From the organs, oxygen-depleted blood, which is filled with carbon dioxide, ends up in the superior and inferior vena cava. This blood is transported to the right half of the heart and thus ends up in the lungs. The carbon dioxide is removed from the blood via the lungs and eventually exhaled. The lungs then add oxygen to the blood during gas exchange. The oxygenated blood is transported from the lungs to the left half of the heart, where the oxygen-rich blood is pumped to the organs again via the aorta.