The vertebrates hearts have the role of pumping blood into the body. Vertebrates possess hearts having different numbers of chambers. Birds and animals possess four chambered hearts, while amphibians and reptiles possess three chambered hearts. The chambers of hearts store and separate the blood rich in oxygen by the blood depleted of oxygen.
Amphibians and reptiles, such as frogs, toads, lizards and snakes, have three chambered heart, one ventricle and two atria. The blood depleted by oxygen is returned by the body into the right atrium, then it goes to the ventricle, which pumps the blood into the lungs, where the blood enriches in oxygen and it gets rid of carbon dioxide, then it returns into heart's left atrium and then it goes to ventricle, which pumps the blood back into the body.
Since amphibians can obtain oxygen, not only from lungs, but from skin, too, the structure of heart has been changed from four to three chambers.