Your storied past has fallen from memory because everyone thought you died. Your Karma is reset, you inflict +10% damage, and for every 100 points of Karma, you gain 10 Health. You are also immune to critical hits. This perk requires you to have good karma.
You cannot gain more than 100 additional Hit Points from this perk, due to positive karma maxing out at 1000.
The bonus HP is applied as an effect, which is visible on the Pip Boy, not as actual modification of your health total.
Bonus HP is not shown on your on-screen HUD in the lower left corner. With full health and 100 bonus HP, for example, the display will not change until you lose more than 100 HP. Your actual current HP is visible on the Pip Boy Status screen.
The bonus HP gained from this perk are calculated based on the player's karma at the moment the perk was acquired. A player who reaches level 50 with 1000 karma will immediately gain the maximum 100 additional HP.
Because the perk requires level 50, it cannot be taken unless you have all four Fallout: New Vegas story add-ons.
Taking this perk causes the karma loss message to appear.
You do not lose the perk as you lose karma. Once you gain it, it is permanent.
xbox360 If you are at full normal health, eating additional food to heal up the bonus HP will actually subtract HP from the HP Healed from Food statistic.
Having any magnitude of this perk (or possibly any additional HP that causes your actual maximum to exceed the reported maximum in the Pip Boy) will cause your character to lose the built in fail safe that normally prevents you from wasting healing items when you are already at full HP even if you are already healed up to your actual modified maximum.