Explain why an amphibian's heart would not be suited to a mammal?

An amphibian's heart typically has three chambers—two atria and one ventricle—allowing for some mixing of oxygenated and deoxygenated blood. This design is efficient for their lower metabolic demands and dual life in water and on land. In contrast, mammals have a four-chambered heart that completely separates oxygenated and deoxygenated blood, supporting higher metabolic rates and more active lifestyles. Therefore, an amphibian heart would be insufficient for a mammal's needs, particularly for maintaining efficient oxygen delivery during sustained activity.