We're not talking about organisms, we're talking about cats, dogs, monkeys, humans . . .
Not initially we aren't. Cats, dogs, and such were *much* later developments than circulatory systems. if you want to look at when circulatory systems were first formed, they were in very simple organisms, not in cats, dogs, monkeys, and humans.
This is probably one of your difficulties with evolution. You seem to think that there were cats *before* there were hearts. In fact, hearts were around *long* before there were even vertebrates.