The term "four-chambered" typically refers to the structure of the heart in mammals, including humans. This heart design consists of two upper chambers called atria and two lower chambers known as ventricles. The four chambers work together to efficiently pump oxygenated blood throughout the body and return deoxygenated blood to the lungs for reoxygenation. In contrast, many reptiles and amphibians have a three-chambered heart, which is less efficient in separating oxygenated and deoxygenated blood. The four-chambered heart allows for a more effective circulatory system, supporting the higher metabolic demands of warm-blooded animals like birds and mammals.