Fortuitous Vigor (Combat)Source Healer's Handbook pg. 14
Your determination and enthusiasm help you shake off the most grievous wounds and soldier on against your enemies.
Prerequisites: Con 13, Combat Vigor, character level 4th.
Benefit: Your vigor pool gains 1 vigor point. Whenever you roll a natural 20 on an ability check, attack roll, saving throw, or skill check, and whenever you threaten a critical hit with an attack, you can spend 1 or more vigor points as a swift action to regain hit points as described in the Combat Vigor feat.