Heart and lungs, artwork. The heart (centre) and lungs (either side of heart) work together to provide oxygenated blood to the body's tissues. Oxygen enters the body via the trachea (top centre). The trachea divides into two broncioles, which repeatedly branch, until they form alveoli. The oxygen diffuses over the surface of the alveoli into the blood stream. This oxygenated blood is carried into the left side of the heart before being pumped around the body, where it becomes deoxygenated. Eventually the deoxygenated blood travels to the right side of the heart. From here, the blood travels into the lungs, where it is oxygenated and the cycle begins again.