You can not target a piece of a muscle, your pec grows as a whole. Stick to heavey pressing movements and let the flys go, unless of course all you want is a pump, then you can do them all day long, but you still wont see any growth from them.

__________________
I don't do this for my family, my friends, women, accolades, pride, or ego. I do it for me and no one else, its just part of who I am.