I have really flat nipples. I would like to have larger more pronounced nipples. Is that possible? I am a hetero male

This could be achieved a number of ways.  Injectable fillers could be used, but the effect would be temporary.  The advantage of this is that is non surgical.  Long lasting fillers such as Artefill could be used, but I would try with a temporary filler first.  A permanent solution could be fat or a dermofat graft.  This is a surgical procedure. 

Thank you for your question.Yes, nipple enlargement is possible using Cook Medicis bio-compatible nipple implants.

To be sure, see two or more experienced,
board-certified Plastic Surgeons for a complete evaluation to make sure you are
a good candidate and that it is safe for you to have surgery.

I hope this helps.