They don't have... hearts? Are you sure you don't mean SOULs? In my experience, those bear a very distinct heart-shape.

[Hmmmm... He's rubbing his chin now. Very interesting. This bears further contemplation!]

...Did somebody take their SOULs? Hearts? Whatever they are! Because from what I've experienced, typically a human SOUL only separates from the body when... erm. Well, let's just say it's unpleasant!