Via Geoffrey West of Santa Fe Institute:

“As animals get bigger, from tiny shrew to huge blue whale, pulse rates
slow down and life spans stretch out longer, conspiring so that the
number of heartbeats during an average stay on Earth tends to be
roughly the same, around a billion. A mouse just uses them up more
quickly than an elephant.”

It has been known since the 1930s that there is a well defined
relationship between the mass of a species and its rate of metabolism.
The metabolic rate of a species is proportional to its mass raised to
the power of three-quarters. This is just one of many scaling
relationships that involve a quarter or three-quarter power and it
holds true all the way from micro-organisms to blue whales. In fact,
West has found that it even applies to the mitochondria inside cells.