Lifegiver

Livegiver or Life Giver is a Fallout, Fallout 2, Fallout 3, Fallout Tactics, J.E. Sawyer's Fallout Role-Playing Game, and Lionheart perk.

Fallout, Fallout 2, Fallout Tactics, and J.E. Sawyer's Fallout Role-Playing Game
Every time your character gains a level, gain an additional four hit points for each rank of this perk. With two ranks of Lifegiver, that's +8 HP each level, which is more than 10 points in endurance would give you!

Although it's not clear from the description, Lifegiver gives you +4 HP when you take it; you could say it works retroactively for the level you just earned.

Fallout 3
You gain an additional 30 hit points.

This perk also gives you unique dialogue choices when talking with some specific characters, like in Oasis, Tree Father Birch.

Lionheart
With each level of this Perk, you gain an additional 6 hit points.

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