What is the difference between a 3 chambered heart and a 2 chambered heart?

2 chambered - fish, pumps blood in a single circuit, from gill capillaries, tp systemic capillaries, back to heart.

3 chambered - amphibians, turtles, snakes, lizards, has two atria, one undivided ventricle, permits blood diversion away from lungs when diving, but some blood from body & lungs mixes in the ventricle when not diving.