Binding of Isaac: Rebirth Wiki

Added in Repentance

Blood Oath is a passive item added in The Binding of Isaac: Repentance.


  • Spawns a familiar that stabs Isaac at the beginning of each floor if Isaac has more than a Half Red Heart Half Red Heart. This drains as much red health as possible without killing him, leaving a half red heart if Isaac only had red health, or none at all if Isaac has soul/black/bone hearts.
  • Although the animation is only a single stab when the triggered, it's treated as taking damage one time per half heart lost. This can lead to synergies with items that activate upon taking damage.
  • For the rest of the floor, Isaac gains about +(0.15 * HeartsLost ^ 2) damage and +(0.1 * HeartsLost) speed, where HeartsLost is the total hearts of damage taken from Blood Oath (half a heart counts as 0.5).
    • This amounts to a max of +20 damage and +1.15 speed if starting the floor with 12 filled hearts (of which only 11.5 are drained).
      • This increases to +21.8 and +1.2 if starting the floor with 12 filled hearts, at least one being a Bone Heart.


  • Isaac can avoid damage from Blood Oath with invincibility, but he won't gain the damage and speed increase if he does.
  • Eternal hearts give the health up before Blood Oath stabs Isaac, draining that extra heart too.
  • It's also possible to use XI - Strength XI - Strength at the beginning of a floor before getting hit by Blood Oath to have one more heart counted in the bonus.
  • If Isaac has only half a red heart, the effect will not trigger at the start of the floor, even if Isaac has soul/black hearts. Having no red hearts at all also prevents the effect from triggering.
  • Works with Keeper Keeper / Tainted Keeper Tainted Keeper leaving his health at one health coin.
  • The damage caused by Blood Oath does not lower the chance for a Devil Room Devil Room or Angel Room Angel Room to appear.
  • While playing as The Forgotten The Forgotten, red health will not be drained if The Soul The Soul was being controlled when entering the floor, or if changed early enough.
  • If Blood Oath is removed (such as with Tainted Isaac Tainted Isaac), any existing damage and speed bonuses will not be removed until moving to the next floor as normal.
    • An exception is after you defeat The Lamb The Lamb and refuse a Victory Lap, the damage and speed bonuses are removed.
  • Upon getting stabbed, any items that trigger upon getting hit will activate multiple times depending on the number of hearts drained.
  • If Isaac has rotten hearts they will only count as half a red heart when Blood Oath activates.


  • Adrenaline Adrenaline: Activates the damage up effect of Adrenaline for the resulting empty heart containers at the start of each floor.
  • BFFS! BFFS!: Adds 2 full hearts' worth of bonuses if any health is drained at all, e.g. losing 1 heart gives the bonuses of 3 hearts. This allows for up to 14 hearts' worth of bonuses.
    • 14 hearts' bonus gives +29.6 damage and +1.4 Speed.
  • Damage-triggered items: Activate a number of times equal to the total half hearts drained.
    • Does not activate the Panic Button Panic Button trinket.
    • Bozo Bozo: Each half-heart lost has a chance of spawning a rainbow poop, allowing for full red heart regeneration.
    • Gimpy Gimpy / Old Bandage Old Bandage /Shard of Glass Shard of Glass: Each half-heart lost has a chance of spawning a full red/soul heart, allowing Isaac to heal back some of the damage immediately if he has high luck or a large amount of hearts lost.
    • Scapular Scapular: Gives Isaac a soul heart if he had only red heart containers upon entering a floor.
  • Magdalene Magdalene + Birthright Birthright: With full Red Health, Magdalene can achieve up to +46.3 damage and +1.75 speed, and up to +49 and +1.8 with at least one heart being a Bone Heart.
  • The Jar The Jar: Red hearts can be stored for use on the next floor.
  • Placenta Placenta: With enough patience, health can be safely restored each floor by waiting in the starting room.
  • Whore of Babylon Whore of Babylon: Activates the Whore of Babylon effect at the start of each floor.


  • Cursed Eye Cursed Eye: The stab will trigger the teleport if tears are charging.
  • Curse of the Tower Curse of the Tower: Not recommended. Spawns 6 troll bombs for each half heart removed, making death highly likely if Isaac does not leave the room immediately after being stabbed by blood oath, and making the starting room unsafe.
  • Gnawed Leaf Gnawed Leaf: Becoming a statue at the beginning of the stage will not drain any red health.
  • Perfection Perfection: The forced damage will not destroy the trinket, or prevent its acquisition.
  • Stem Cell Stem Cell: The healing will occur before any health is drained.
  • Tooth and Nail Tooth and Nail: Item being active while the dagger falls will not drain any red health.

In-game Footage[]


  • This item is used in Bloody Mary (challenge #37).
  • The familiar will appear much bloodier when a large amount of hearts are drained.
  • This item originated from the Community Remix mod for the original Binding of Isaac game.


PC Normal and hard modes only A088 LA10 (Curse Room adjacent to spawn)


Bug Bug! Using Glowing Hour Glass Glowing Hour Glass to return to the previous floor twice will cause Blood Oath to activate an extra time, giving buffs corresponding to drained HP.
Bug Bug! Upon coming back from obtaining Knife Piece 2 Knife Piece 2, the stat boost obtained from this item at the beginning of the floor will be gone.