Giraffes breathe in oxygen and release carbon dioxide just like humans and other mammals do. When a giraffe breathes oxygen into its body, the air travels down the trachea and into the lungs. The lungs fill up with oxygen, and the giraffe's circulatory system takes this much-needed gas to the rest of the giraffe's body. When a giraffe breathes out, carbon dioxide is released into the air, which the trees and plants need for photosynthesis.

A giraffe's lungs are about eight times larger than a human's lungs because if they were not, a giraffe would breathe the same air over and over again. Since the giraffe's trachea is so long and narrow, there is a big volume of dead air in the giraffe. However, the giraffe's breathing rate is about one-third slower than man's breathing rate to help with this dead air problem. When a giraffe takes a new breath, the "old" breath is not totally expelled yet. The giraffe's lungs must be larger to accomodate this "bad" air and still allow its respiratory and circulatory systems to get oxygen to all parts of its body.

A giraffe's heart is also larger than a human's heart since it has to pump oxygen-rich blood up 10 feet to its brain from the lungs. This takes about double the normal pressure required for the human heart to pump oxygen-rich blood to a human brain. Another interesting thing about the giraffe's body, then, is that when the giraffe lowers its head to get a drink of water, it does not literally blow its top. The giraffe has reinforced artery walls, bypass and anti-pooling valves, a web of small blood vessels, and sensors that give the brain just enough oxygen-rich blood.