Why the larger an animal is, the slower it's heartbeat usually is. For instance a mouse heart beats at approx 600-700 times a minute, a human heart about 70 to 80 bpm, an elephant at 30 bpm and a blue whale at 2 bpm.
I get that the heart is bigger so can pump more liquid in one pump, but the body will also be bigger so shouldn't that balance it out?
Guessing it's something to do with properties of liquid within vessels, but still don't get why the increased body size element doesn't counter that.