This program explores the need for multicellular animals to have specialised internal transport systems. Following veterinary experts, we get an exclusive insight into the day-to-day activities of domestic animal health. Seeing what they do to save the life of that beloved family pet and at its core we see how the transport systems can efficiently distribute materials to and from all parts of the body, providing nutrients to cells and removing waste products. They also provide the vital link with the exchange (respiratory and excretory) systems. The evolutionary aspect of internal transport mechanisms is discussed. Following this is a detailed look at circulatory systems, including the differences between the closed systems of vertebrates and the open systems of invertebrates.