Unbreakable Heart - Avoids death from a death blow, health will stay at 1 HP.
Type: buff - Category: Shield, Death
See also: | 
Aegis Shield | 
Blending In | 
Damage Reflection | 
Ethereal Spirit | Invincibility | 
Shrouded | 
Unbreakable Heart
Heroes
The following heroes have or can inflict/apply Unbreakable Heart:
Slow Poke (Trait): Attacks last, but Max Health and DEF are increased by [25%], and this Hero will also take no damage from the first killing blow. (Percentage is increased by Skill.)
Tooth And Nail (Special Attack): 3 Armor-Piercing Melee Physical attacks on target enemy, then gains Unbreakable Heart for 3 turns. Switches to 'To War!: Cavalry'.
Unbreakable Heart (Trait): Avoids death from the first death blow, health will stay at 1 HP. NOTE: There is also a identically named Buff in the game. Runes can add this Trait. Shield-piercing attacks ignore Unbreakable Heart.
Last Stand (Special Attack): Melee Physical attack on target enemy with splash damage that grants the team Unbreakable Heart for 3 turns.
Immunity
The following heroes are immune to Unbreakable Heart:
Chaos Missile (Basic Attack): Basic Ranged Chaos attack on a single target. Chaos Damage is shield and armor-piercing and it cannot be dodged or parried. It ignores the five Elemental Resistances as well as Damage Reduction. But never scores a CRIT.
Cataclysmic Conflagration (Special Attack): Sacrifices self, dealing shield-piercing damage to all enemies with 100% base chance to purge all buffs and add Soulfire Burn to enemies hit. Removes all enemy corpses. Can't be dodged.
Solar Flare (Special Attack): Shield-Piercing Ranged Light Attack on all enemies for [??% ATK] base damage with 100% chance to Blind. Consumes all stacks of Solar Scales, and deals additional damage based on the number of stacks consumed. Starts Powered.
Infernal Inferno (Special Attack): Shield-Piercing Ranged Fire attack on all enemies that ignores Damage Reduction and inflicts Demonfire Burn on hit (damage over 2 turns, cannot be cleansed).
Windows to the Soul (Trait): All attacks are Shield-Piercing and will heal [25%/50%] of damage dealt (% healing increased with Skill). The percentage value depends on the rank (I-II) of the trait.
Storm of the Ancestors (Special Attack): Shield-piercing ranged lightning attack on all enemies, consumes all stacks of Storm Power, dealing 10% more damage for each Stack of Storm Power. Adds a Buff to all allies that increases their damage to Shocked or Paralyzed targets.
Arcane Bolts (Special Attack): Armor-Piercing and Shield-Piercing Ranged Spirit attack on all enemies.
Chaos Missile (Basic Attack): Basic Ranged Chaos attack on a single target. Chaos Damage is shield and armor-piercing and it cannot be dodged or parried. It ignores the five Elemental Resistances as well as Damage Reduction. But never scores a CRIT.
Demolishing Smash (Special Attack): Armor-Piercing and Shield-Piercing Melee Physical attack on target that Wounds target enemy. Starts Powered. 
Doom Bolt (Special Attack): Shield-Piercing Ranged Lightning attack that deals 1.5x damage against Armored tagets. If target dies, the corpse is removed.
Murky Shield (Special Attack): Shield-Piercing Ranged Dark attack that grants self Murky Shield, becoming Paralysis and Silence Immune for 3 turns. Enemies cannot Revenge while Murky Shield is activated.
Living Stone (Trait): Immune to all debuffs but can be healed normally.
Construct (Trait): Cannot be healed but is invulnerable to all Debuffs.
Construct (Trait): Cannot be healed but is invulnerable to all Debuffs.
Construct (Trait): Cannot be healed but is invulnerable to all Debuffs.
Dryad Ice (Trait): Starts dungeons in Ice Block, reducing damage taken (90% Damage Reduction) and Debuff immune until their first turn. Can't be stolen, copied, or purged.
You Can't Catch Me! (Trait): Flying allies can't have buffs removed or debuffs added by non-Flying enemies.
Ambush Tactics (Special Attack): Ranged Physical attack on target enemy and all Ranged allies attack the same target, then gain Stealth and become Invulnerable for 1 turn. Starts Powered.
Ice Block (Trait): Starts dungeons in Ice Block, reducing damage taken (90% Damage Reduction) and Debuff immune until his first turn. Can't be stolen, copied, or purged.
Living Stone (Trait): Immune to all debuffs but can be healed normally.
Construct (Trait): Cannot be healed but is invulnerable to all Debuffs.
The Last Word (Trait): Slow allies and self take 30% reduced damage from Fast enemies. Slow allies revenge attacks twice. Slow allies can't have buffs removed or debuffs added by fast enemies.