I have a strong feeling running 5 undergeared shamans in a heroic won't cut it. If you really wanna jump in heroics do like Anozireth said and drop one shaman for a tank. My 4 shamans just dinged 70, but i've been around the block before so I had them honored in the big 5 factions before even turning 70 (Cent exp, thrall, lower city, shatar, and Keepers of time). When i dinged 70 I put them in full pvp blues, plus whatever quest rewards they had from leveling. At around 370 spell damage they can DPS heroics with a proper tank. Make sure your tank is at least raid geared (aka kara) and you should be able to pull it off.

Knowledge of the instances is pretty key too your success. Yesterday i let my girlriend play my paladin, (she's never played wow before in her life and after months of coxing she finally caved in) and she healed my tank (kara+badge gear) and my three 370 spell dmg shamans with much success. That paladin only has 700 healing (pvp blues and leveling quest rewards). It was underbog and i knew it like the back of my hand, the only time we wiped is when she moved too close to a naga patrol route and Ididn't warn her; Just to mix it up some. She was bored because i'd say exactly where to stand and what was lying ahead. I was so proud of her when she stunned one of the adds but then she was so excited she forgot to continue healing. lol.