Improved Mettle Training (3.5e Feat)
From D&D Wiki
Improved Mettle Training [Epic]
You are able to resist effects with even greater fortitude.
Prerequisite: Con 15, Great Fortitude, base fortitude +3, Mettle Training or Mettle from a class source.
Benefit: If you succeed on a Fortitude save against a spell or effect with a partial effect on a success, you instead suffer only the partial effect on a fail. On a successful save, you suffer no effects from the attack.