Well... initially i had my right chest, and right arm bigger than my left side. So to correct this I would bench press with either a 2.5 or a 5 pound weight on the left side, and i would always nail out a few more reps with my left arm when I did alternating curls. Now.. my left chest and left bicep is alittle bigger than my right. As far as my arm goes, i do not mind since i would like my left to be bigger and my right to be more cordinated. I guess you could do like I did with the bench, or with dumbbell flyes you could use a slightly heavier weight on your left side. But its not something to worry about nor is it uncommon.. its like one ball or boob hanging a little lower or being a little bigger than the other.. nothing really too worry about unless you have a MAJOR disproportion. hope this helps ya.