I'm almost positive that the hearts don't cycle. There are simple DEs that are tied to, or at least in the same area as, several hearts.
Some hearts have general objectives such as "keep the area safe from threats" or I don't know how they word it.
Anyway, time will tell if I remember wrong or if you do, I admit that I am not 100% sure about it either. Not that it matters really, I am not sure why I brought up that hearts cycle in the first place.
edit: Oh yeah, I just checked, because it would give more of an illusion of having an important (if local) role to play.