How different is the amphibian heart from the fish heart?
The fish heart has only two chambers, a ventricle and an atrium, and the blood that comes to it is purely venous.
In amphibians there are three heart chambers (a second atrium is present) and there is arterial blood coming from the lungs; in these animals the heart has two atria (one that gets blood from the body and other that gets blood from the lungs) and one ventricle; arterial blood mixes with venous blood within the ventricle which in turn pumps the blood to the lungs and to the systemic circulation.
Frog Facts Review - Image Diversity: amphibian heart