/Patch 4.0.1 (2010-10-12): Cooldown increased to 5 minutes, up from 3 minutes. Duration decreased to 12 seconds, down from 20 seconds. Now, instead of adding to health, this ability now grants 60% damage reduction for it's duration.
Patch 3.1.0 (2009-04-14): Cooldown reduced to 3 minutes, down from 5.
Patch 3.0.8 (2009-01-20): Now temporarily grants you 30% of your current maximum health for 20 sec. (Old - 30% of your maximum health)