It's hard enough running normal instances with 5x shaman nevermind heroics.

I did violet hold last night, twice with 5xshaman... (at level 77). Wiped on the first boss both times.

I then switched to 80 warrior and 4x shaman. No characters died until i got to the last boss and wiped from my own fault of *ahem* not healing.

If you want to do instances, you really need a tank.