I was able to do Loken on Heroic successfully by healing through his AoE nova. Stand on top of him during the fight.

The nova hits for 10638-12363 (according to wowhead) on heroic. I did check my combat log and notice it doing ~15k dmg several times, but NR totem helped.

I had my tank use commanding shout and my shammies were just about 15k-15.6k life. Make sure you drop NR totem.

Its essentially the same as regular, except his periodic AE pulses seem to get stronger further along. You WILL need to top off everyone before his Nova hits, I would spam CH several times (just in case his periodic AE hits right before the nova).