Straight-cut, heavy bangs may be a trendy look, but it's not one that lengthens your face. Blunt bangs draw a line across your face, making your face look both shorter and wider. So, if you have a round face, it's best avoid to avoid this hairstyle.
If you simply must have heavy straight bangs, at least make sure you have some height on top. We're not talking Snooki from "Jersey Shore" or anything, but a little volume at the top of your head will add the illusion of length to your face. You could also have your hair stylist cut side-swept bangs, a softer bang look.