Question

why do mammals have 4 chamber heart while amphebians and reptiles do not?

Answer 1

mammals have 4 chamber heart to transport the oxygenated and deoxygenated blood from mixing so that there is a sufficient supply of oxygen

Answer 2

For one thing, amphibians are extremely small compared to most mammals, and it wouldn't be capable of pumping the vast volume of blood in mammals before wearing out.

Second, amphibian hearts are 3 chambered, and mammalian hearts are 4 chambered. Since mammals regulate their own body temperature, they need a more efficient system which separates the deoxygenated blood more completely from the oxygenated blood.