>The lower efficiency of a bigger heart would require a higher contraction frequency to compensate If that's the case, then how come rats have a higher heart r

>The lower efficiency of a bigger heart would require a higher contraction frequency to compensate If that's the case, then how come rats have a higher heart rate than humans, who have a higher heart rate than whales? Do whales have hearts with thinner walls than humans, while rats have big lumps of muscle with teeny tiny chambers?