I would advise any woman who is leaning towards heavy cleavage in her wedding gown of going towards a more modest approach. I believe your wedding day is meant to be fun and beautiful, with family and friends to join in the celebration. You can feel sexy while still keeping a modest chest, and save the revealing outfits for the wedding night.
Say you've found a wedding dress you love, but the cleavage is more than you would like. You can always have the dress altered to fit your ideal, or you can find something similar that is a bit higher necked. Building out a V-Neck so it hides cleavage is a task most tailors and seamstresses can take on with no problem, it's likely you'll need the dress altered anyway, for fit and height.
I say "No" to too much cleavage, how about you?
