Fortitude Dying Resistance (3.5e Variant Rule)

Fortitude Dying Resistance
The weak bodied wizard with Con 8 and the tough as nails barbarian with Con 20 both perish as soon as they hit -10 hp, it's rather strange. However with Fortitude Dying Resistance, the barbarian gains the advantage for having a strong Fortitude save.

When dropped below 0 hp, a creature must make a Fortitude save against the amount of negative hp they have. A character dropped to -7 hp would need to succeed on a DC 7 Fort save, or bleed out losing 1 hp and increasing the save for the next round. If the character fails 3 saving throws in a row, they die. If they succeed they stop bleeding and are stable. A heal check made as a full round action can be used to substitute the Heal check result with the Fortitude save for the dying character, if higher.

This has three major effects. Characters now die much less often if they roll a natural 20, even if deep into the negative hit points, or due to the aid of allies and their Heal checks. The other effect is that Fortitude heavy characters have a much better chance of recovering over the typical Will based caster. Lastly characters are generally slightly tougher than normal, as even +0 Fortitude characters can potentially survive high damage if they're lucky.

The Diehard feat allows the character to act normally as long as they make their saving throws. If they fail one of the saves, they fall unconcious and are dying until they make another successful save or they die.