In mammals, the heart is separated into four chambers. This anatomical structure, consisting of two atria and two ventricles, allows for efficient separation of oxygenated and deoxygenated blood. The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs for oxygenation, while the left side receives oxygen-rich blood from the lungs and distributes it to the rest of the body. This four-chambered arrangement is vital for maintaining a high metabolic rate, supporting the energy demands of warm-blooded mammals. Birds also share this four-chambered heart structure, indicating a close evolutionary relationship.