My entire team is currently at 5 hearts. I made sure of that before challenging the Elite 4, just to maximize the benefits.
Also, be careful when petting your Pokemon. You might accidentally punch them in the face or something.
Then again, some Pokemon don't seem to mind. I once punched Sharptooth the Tyrantrum in the face three times in a row on accident, but he didn't seem too angry about it. I think he knew it wasn't on purpose lol