Hearts? Well... if you're talking about the organ, sure I know about them.

[But something about the way Roxas is talking about it makes Aang think that that's not what he's referring to. He sits down next to Roxas and rests his glider next to him.

He has questions about jumping through worlds, but for now, it seems like talk of hearts are more important.]

And... well, I know that 'heartless' means someone who acts like they don't have a heart.