3 chamber hearts: Frogs and toads
Amphibians such as frogs and toads have 3 chambered hearts. 2 atrium's and one ventricle. The oxygenated blood from the lungs goes thought the left atrium and at the same time the de-oxygenate blood from the body goes though the right atrium, both of the atrium's empty into the ventricle where the oxygenated and de-oxygenated blood gets mixed together. Amphibian animals only have 3 chamber hearts because they have lower metabolisms and require less oxygen. The reason why 3 chamber hearts are not as efficient as 4 chamber hearts is because the animal that has the 3 chamber heart such as a frog do not need to have such an efficient heart like a mammals who need more oxygen. Also because animals likes frogs and toads obsorbe the oxygen through there skin.