> Bigger bodies can evolve together with bigger hearts, as already witnessed with the very whales being researched.

Hm? Aren't blue whales the biggest animals to ever have lived that we know of?

Yes. There are many extinct animals that had sizes comparable with sperm whales, including some dinosaurs, but none of them had sizes comparable with blue whales.

The reason for this is simple, few animals have developed a method of feeding like that of the baleen whales, by filtrating huge amounts of sea water, which can provide enough food for such a huge body.

Other animals that have developed similar feeding methods, like 4 groups of species of sharks or rays, including the whale shark, have also become much bigger than their relatives.