Lifegiver

Livegiver or Life Giver is a Fallout, Fallout 2, Fallout 3, Fallout: New Vegas, 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, you 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, Fallout: New Vegas
You gain an additional 30 hit points.

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

Lionheart
With each rank of this perk, you gain an additional 6 hit points.

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