Amber Heard hasn't had breast implants, she's just put on a little more weight than her earlier roles - and has started using a bit more padding and more supportive bras.
If you really want to examine Amber Heard's breasts, just take a look at some of the more revealing outfits she's appeared in recently:
Now compare her breast size there to the 2008 film The Informers (where she gets completely topless - NSFW by the way!!!)
Is there really that much difference? I believe that if she'd gone to the trouble of cosmetic surgery on her breasts, you'd know for sure whether they look considerably bigger or not.
The fact that it's difficult to tell suggests Amber heard's boobs might have grown slightly over the years, and some of the low cut outfits she wears are designed to make the most out of her cleavage. Case closed!