Here is a strategy I found posted on wowhead.com
Heroic Lord Ahune is, in my opinion, THE most difficult heroic fight Blizzard has implemented, and they should be proud. To kill him, you should clear the pack of 3 naga and a sporebat, the 3-naga pat, the slavehandler, and the 4 Lobstrok in the middle of the area - Ahune himself will spawn the other side of them, and them being alive pretty much guarantees a wipe.
Phase 1:
A large Ice Elemental will spawn, followed by smaller water elementals, 2 at a time. Set a melee DPS, if you have one, to small ones, and have the rest nuke big one. Big one has an aura, 300 dmg/3 secs, stacking up to 10 (1k dps), so try not to bring too many melee or you're in trouble. Smaller adds don't do much dmg or have much health, but can quickly overwhelm the party, thus the melee on them.
Additionally, small rings of ice will appear on the floor troughout this phase, which will turn into large icicles after a few seconds, dealing approx 2k damage and knocking anyone hit into the air - so move away!
After the large add dies, no more if it will spawn, but small ones will continue - tanks can help kill them (druids go kitty, etc).
Phase 2:
Lord Ahune will retreat into his core, which you can then nuke. Blow all your CDs - this needs to go as low as possible, 40% is a good number to aim for. After a lil of this, he will move to p3.
One thing to be aware of - the ice around him can cause you to Slip Up, which is really a 1 second knockdow/stun.
Phase 3:
Same as phase 1, but an air elemental will spawn with water ones. Its no real problem, just an extra add to deal with and something to be aware of.
If you don't kill him in 2 cores, you are in trouble, and likely running OOM (similar to Ragnaros).
When he dies, a chest will spawn which contains an epic and the pattern for Enchanting Deathrost, and the chance for a small pet, the Scorchling (in normal, i've only ever got 1 epic, although I assume theres a chance for pattern/pet). Also, Shards of Ahune (which start a quest for a tabard), a badge, and some Huge Snowballs, which are like normal ones with a bigger animation and a higher arc when thrown.
Good luck!