This interactive module explores the circulatory systems of major vertebrate groups to gain insights into their evolution.

Over millions of years of vertebrate evolution, the heart has changed dramatically from a relatively simple two-chambered heart in fish, to a three-chambered heart in amphibians and reptiles, and to a four-chambered heart in mammals and birds. This Click & Learn allows students to compare the circulatory systems of eight different vertebrates, including their heart structure and function.