Which animal most likely has a 3-chambered heart?

• A. Lizard
• B. Crocodile
• C. Bird
• D. Mammal

Answer: (A)

Three-chambered hearts are typical of many non-avian reptiles and amphibians, where there are two atria but only one ventricle. This setup allows some mixing of oxygenated and deoxygenated blood, which is characteristic of reptiles like lizards. Birds and mammals, in contrast, have four-chambered hearts with two separate atria and two ventricles, keeping blood streams fully apart for efficient circulation. Crocodilians also have a four-chambered heart in practice, despite specialized structures that can reduce mixing. So, among the options, the lizard is the one most likely to have a three-chambered heart.