Welcome to the "Vertebrate Circulatorium." Here you can compare the circulation patterns of different vertebrates. Click on the different animal names on the left to see the overall circulation patterns in "systemic view." More detailed views of the hearts are available by clicking on "To heart detail".

As vertebrates evolved from aquatic to terrestrial forms, circulation patterns became more complex. The most ancient group, the fish, has an undivided heart that pumps the blood through the gills to the rest of the tissues.

In the youngest group, the birds (but also in mammals), the heart is divided so that one side pumps blood to the lungs (pulmonary circulation) and the other to the rest of the tissues (systemic circulation). This change from an undivided to a divided circulation occurred as a consequence to the change in lifestyle from aquatic to terrestrial habitats.