The term "three-chambered" typically refers to the heart structure found in certain animals, such as amphibians and reptiles. Unlike mammals, which have a four-chambered heart, these animals possess three chambers: two atria and one ventricle. This design allows for some mixing of oxygenated and deoxygenated blood, which is less efficient than the separation found in four-chambered hearts. In amphibians, the three-chambered heart supports both aquatic and terrestrial life stages, facilitating gas exchange in both environments. In reptiles, the heart is more advanced, with partial separation in the ventricle, improving oxygen delivery during activity.