Double circulation refers to the circulation of blood through the heart twice during each cycle. Other vertebrates, such as birds and mammals, exhibit double circulation, with blood passing through the heart once to the lungs or gills for oxygenation and ...

Fish have only two chambers in their hearts, which pump blood directly to the gills for oxygenation before it is circulated to the rest of the body.

Animals that do not use energy to maintain body temperature, like amphibians and many reptiles, can tolerate some mixing of oxygenated and deoxygenated blood. Therefore, they have three-chambered hearts.

Animals with high energy needs, like birds and mammals, require a constant and efficient supply of oxygen to maintain their body temperature, which is facilitated by the separation of the heart.

The separation prevents oxygenated and deoxygenated blood from mixing, ensuring an efficient supply of oxygen to the body.