How many chambers does a snake's heart have?

A snake’s heart has three chambers: two atria and one ventricle. The right atrium receives oxygen-poor blood returning from the body, while the left atrium receives oxygen-rich blood from the lungs.

The single ventricle is not simply an undivided cavity. Internal muscular structures separate it into interconnected regions that help direct oxygenated and deoxygenated blood toward the appropriate circuits. This arrangement supports a functional double circulation despite the incomplete separation.

Snake hearts are also adapted to their long, flexible bodies. The heart sits inside a protective sac called the pericardium and can shift position as large prey moves through the esophagus. Snakes lack a diaphragm, so this mobility helps reduce the risk of compression during swallowing.

The three-chambered arrangement is typical of snakes and most other reptiles. Crocodilians are the notable reptile exception: they have fully separated four-chambered hearts, like birds and mammals.