Arcane Toughness( Player's Handbook II, p. 75)
You draw upon the power of your magic to sustain yourself, allowing you to continue fighting long after your physical body has failed you.
Toughness (PH) , arcane caster level 3rd,
Arcane Consumption (PH2) ,
You can expend a prepared spell or spell slot as an immediate action when you are reduced to 0 or fewer hit points. You heal a number of points of damage equal to the level of the spell or spell slot used in this manner. You cannot use this ability to negate effects that disable you without causing hit point damage, such as a medusa's ability to turn you to stone. Even if this healing does not bring you above negative hit points, it still stabilizes you. Using a 0-level spell with this feat grants no benefit.