It is necessary to separate oxygenated blood from the deoxygenated blood in mammals.

i. Mammals require constant supply of energy to maintain their high body temperature.

ii.          Due to this they have high energy need. This energy is supplied through oxygen rich blood.

iii.         Therefore oxygenated and deoxygenated blood should not mix with each other.

iv.        In mammal's heart, these two types of bloods are separated by the septum in the heart and thus they have highly efficient supply of oxygen to the body.