Hey guys! First off, two points. I tested this about a week ago and it worked, (both me and another DK did it) but it may be fixed now, not sure (can't get the same acheivement twice). Also, not sure if this is a repost, I looked around but couldn't find any.
Okay, so what I was doing was farming alterac valley and strand of the ancients for honor for my first time when I hit 80 with my death knight. I joined Strand of the Ancients, and Alterac Valley, and WSG que. When WSG popped, I joined and it was already beginning. I run down and see a paladin, I use my two diseases and then death strike to get myself some health, then suddenly it tells me I get the acheivement to heal 300,000 points in a BG. I was talking to another DK friend, and he did the same thing as me (joined the 3) but for him alterac valley popped. When he joined he faught a guy, and his ghoul was low health, so he used ghoul frenzy and instanly got it. I checked my "healing done" in the BG scoreboard and it was i think 2-3 thousand, when the acheivement needs you to be at 300,000. Hope this helps!
Okay thats the back story ^^^^^^^ let me show you the step by step guide.
1. Join que for THREE BATTLE GROUNDS!
2. Join the first one that pops up and run as fast as you can towards someone of the opposing faction.
3. Attack them, then use a move that heals you, a minion, or maybe even anotehr player (untested), and then watch the acheivement fill itself in.
KK, see yall!