Question

Why do small animals have faster heartrates

Answer 1

Smaller organisms have higher ratio of surface area to volume. So, they lose body heat rapidly and have to generate more heat fast to maintain their body temperature. So, their hearts beat faster to redistribute body heat to maintain the homeostasis

Answer 2

Small animals have faster heart rates than large animals because their metabolism is faster, which means they need more oxygen to generate energy. Since their size is small, the oxygen supply is limited, and the only way to make up for it is by pumping more blood through their bodies at a faster rate. Additionally, small animals usually have a higher surface area to volume ratio, which means they lose more heat through their body surface, so they need to increase their metabolic rate to generate more heat. All these factors contribute to small animals having a faster heart rate.