Regardless of the size of the animal and his heart ritma
Heartbeat appears for each individual - for example, in the moments of excitement or exercise pulse rate, and while sleeping or resting heart beats slower. If you look at the problem more broadly, for every type of heart rhythm should be different - from small animals the heart has to beat faster than larger.
From this it follows that the number of heart contractions over a lifetime test, should be different for each type, but this is not so. Living beings, despite their differences, have a similar number of heart rate during his lifetime - that number is about 1, 5 billion times.
Large animals live longer, but their heart beats slower, and small animals live on less, and their heart beats more often. Thus, most of the species of living beings has roughly the same number of heartbeats in a lifetime.