Tetrapod probably had a three-chambered heart, as do modern amphibians and reptiles, in which oxygenated blood from the lungs and de-oxygenated blood from the respiring tissues enters by separate atria, and is directed via a spiral valve to the appropriate vessel — aorta for oxygenated blood and pulmonary vein for deoxygenated blood. The spiral valve is essential to keeping the mixing of the two types of blood to a minimum, enabling the animal to have higher metabolic rates, and be more active than otherwise. The difference in density between air and water causes smells (certain chemical compounds detectable by chemoreceptors) to
Experiments in the Revival of Organisms is shown being isolated from a body; four tubes connected are then connected to the organ. Using an apparatus, the heart beats in the same manner as if it were in a living organism. The film then shows a lung in a tray, which is operated by bellows that oxygenate the blood. Following the lung scene, the audience is then shown a heart-lung machine, composed of a pair of diaphragm linear pumps, venous and arterial, exchanging oxygen with a water reservoir. It is then seen supplying a canine head with oxygenated blood. The head is presented with external stimuli, which