Technically. Nature abhors a vacuum, however; a heart begins to reform once you've lost it, but it has to be nurtured. It's not the same as one's physical heart. And it's worth mentioning that being without a heart essentially makes you an abomination unto nature.

[Ienzo hesitates for a long moment.]

Namine can manipulate memories of those related in some way to Sora, but it isn't something that gives her any pleasure.