This article describes a variant of the Vitality and Wound Points rules from Unearthed Arcana Chapter 4: Adventuring.
In considering how to synthesize d20 and HERO system, I considered various hit point and damage models. Vitality and wound points look like they come close, with some modifications.
Vitality points behave much like standard hit points. At each level (or hit die) a creature rolls his hit die and adds the result plus his Constitution modifier (with a minimum of one) points to his vitality point total. At first level (or hit die) elite creatures (PCs or important NPCs and creatures) gain maximum hit points.
Wound points measure how much ‘real damage’ a living creature can take. A living creature starts with wound points equal to its Constitution score plus Strength modifier (minimum 1), and gains an additional wound point at each level or hit die. Unliving creatures (constructs and undead) have no wound points).
Dying points are taken after all wound points have been used. A character has a number of dying points equal to his Constitution score, without considering Strength modifier.
 I want strength — muscle, strength, and simple *meat* — to have some effect on how much abuse a creature can take. Generally, those who are more muscular can take more damage and still function than someone less muscular but otherwise ‘in similar health’.
 I need a better name for this.
Almost everything that currently does hit point damage does vitality damage. When vitality points have all been removed by damage, additional damage is done to wound points. Damage to vitality points has no effect on a creature’s abilities.
Damage to wound points is generally done after all vitality points have been removed by damage or by criticals. When a creature has wound point damage it is limited to a single partial action per round unless a Will save is made each round (DC 5 + wound damage). If successful the creature can act normally for the round. A new save may be made each round, regardless of results of previous saves.
When a creature has taken more wound damage than it has wound points, it falls unconscious and is dying, taking another point of dying damage each round until a DC 15 Fortitude save is made or the dying damage exceeds dying points and the creature dies. If the save is made the creature stabilizes; taking additional damage destabilizes the creature again. I may change this back to the UA version (save or die; save by less than 5 maintain; save by more than 5 and less than 10, stabilize but remain unconscious; save by 10 or more, stabilize and become conscious).
Constitution damage does not affect vitality or wound point totals, though Constitution drain will. Intelligence damage doesn’t reduce skill point totals, I do not feel it necessary to deal with adjusting vitality, wound, and dying points with Constitution damage.
 I want mental toughness and willpower to have an effect on damage. This is done by requiring a Will save here rather than a Fortitude save. A Fortitude save would also be appropriate, but these rules make Constitution very, very important to the damage system and ignores willpower effects.
 In play, I don’t track current vitality and wound point totals. I track the damage and compare damage to points, ‘spilling over’ when needed. This is simpler than tracking current totals. Temporary damage comes up infrequently enough that I find comparing ‘damage + temp’ to total points a small price to pay for always adding in the common case.
For the simple bit, a critical hit does normal damage (non-multiplied) directly to wound points, bypassing vitality. Additional damage from ‘rolled sources’ (such as sneak attacks or flaming weapons) is done to vitality.
I’ve got a couple of ways of handling critical hits from weapons that have damage multipliers greater than x2. Unearthed Arcana trades the increased multiplier for expanded critical range. I don’t like this much.
One option is to roll the additional damage (beyond the x2, so a battle axe would ‘roll normal damage once’) and apply it to vitality. The weapon does more damage than usual, but to vitality. Without this, a single critical could *easily* flatten many creatures… a little more dangerous than I want.
Another option is that each multiplier beyond 2x increases weapon damage as if the weapon were one size larger. For instance, on a successful critical a medium battle axe (d8, 20/x3) would do damage as a large battle axe (2d6+modifiers). A medium heavy pick (d6, 20/x4) would do damage as a huge heavy pick (2d6).
A night’s complete rest (8 hours of sleep) will remove a number of points of vitality damage equal to the character’s level (number of hit dice) plus Constitution bonus, and one point of wound damage and one point of dying damage. A full day’s rest (24 hours of ‘bed rest’) will double these.
Healing spells in my campaign provide one day’s healing per spell level. Lay on hands provides one day’s healing per application.
If using my augmented spells system, Cure Wounds may be cast with a +1 augmentation that causes it to work directly on wound points instead of vitality points, and a caster with the Great Healer feat may use a +2 augmentation to work directly against *both* wound and dying damage.
Diehard (Wound/Vitality) [Martial]
Benefit When wounded, you automatically succeed at all saves to act normally. When you have taken dying damage, you automatically stabilize.
Normal When wounded, you must make a Will save (DC 5+wound damage) each round or be limited to a single partial action.
Toughness (Wound/Vitality) [Martial]
Benefit You gain one additional hit point per Hit Die, one wound point and one dying point.
Special You may take this feat multiple times; its effects stack.
Note Toughness IMC gives one additional hit point per hit die, rather than +3 hit points as in RSRD.