Fishes: The heart of fishes has two chambers, an auricle and a ventricle. The deoxygenated blood enters the auricle and is transported to ventricle from where it reaches the gills for the process of oxygenation. From here the blood is circulated in the body. This is an example of single circulation where the blood crosses the heart only once.

Frogs: Amphibians have a three chambered heart, two auricles and one ventricle. This means that the oxygenated and deoxygenated blood gets mixed up and causes an insufficient supply of oxygen to body cells.