Since the heart has to pump enough blood to all tissues in the body to meet the demand for nutrients and oxygen, heart rates (beats per minute) match the cellular metabolic rates: they are faster in small species and slower in large species. But since small animals also die earlier than large animals, the total number of heartbeats in a lifetime are the same across species, from the tiniest shrews to the mightiest whales. We all get about one billion heartbeats.
