Why do smaller animals have faster
Smaller animals are constantly on the lookout for danger
and must be able to react quickly when they need to.
A fast heart and breathing rate ensures
that enough oxygen is being put into the bloodstream to allow the animal to move quickly without getting tired, or eaten.
Also, because the animal is smaller, it doesn't take the blood very long to travel one loop around
the circulatory system, as it might if it were an elephant or a whale.
The circulation is therefore
quicker allowing the heart less time to relax in between pumps.