Deathless Master

Combat

Even if you suffer a grievous wound, you can shrug off the damage and continue your relentless assault.

Prerequisite: Str 13, Con 15, orc or half-orc, Deathless Initiate, Diehard, Endurance, Ironhide**, base attack bonus +9.

Benefit: When you are at 0 or fewer hit points, you do not lose 1 hit point when you take an action.

Source: Ultimate Combat