If Isaac enters a room with a half Red Heart or less, a pool of urine (blood in Eve's case) will be formed under him.
In order for Isaac to pick up Red Hearts, he must have Heart Containers that can be gained from a number of "Health Up" collectables or through completion of an Eternal Heart. Most characters also begin the game with at least one Heart Container, with the exception of ???, who is unable to gain Heart Containers at all, instead converting them into single Soul Hearts. Upon taking damage, Isaac will lose Red Hearts and be left with unfilled Heart Containers, which can then be refilled by the collection of Red Hearts.
After earning a 12th Heart Container their icons shrink, allowing for more to be visible on the health bar. However, it's not possible to have more than 16 Heart Containers, as any HP up earned at that time will be turned into a Soul Heart instead of a Heart Container.
Soul Hearts look similar to regular hearts but are blue with a faint white outline. They are a rarer form of Heart which may replace nonspecific Red Hearts, or can be found in Shops. They have a high chance of spawning when a Tinted Rock is blown up.
Soul Hearts function as a form of armor for Isaac, absorbing damage that he takes so that he does not lose any Red Hearts. Once a Soul Heart is obtained, most damage removes Soul Hearts until their supply is depleted. Each Soul Heart adds a full Heart and can take a full Heart's worth of damage before being lost. Soul Hearts may be increased beyond the maximum visible level of Red Hearts and will still be counted even though they are not shown. The last half Soul Heart Isaac has will absorb any amount of damage while breaking, so taking a full Heart of damage with one half Soul Heart will not affect Isaac's Red Hearts.
Additionally, three Soul Hearts may occasionally be traded in the Devil Room in exchange for a Collectable (for characters without heart containers, like Azazel and ???, all devil deals are traded for soul hearts).
A Heart has a chance of spawning as a Soul Heart based on these rules:
- 1/10 chance
- 1/6 chance if playing as Eve (16.25%)
- 1/10 if holding the Mom's Pearl trinket
- 1/2 if holding the Mitre
Note that the extra chances for a Soul Heart to spawn are consecutive rather than additive, so (if not Eve) with Mom's Pearl, Isaac's chance would be 1 - (0.9 * 0.9) = 19% (rather than 20%) and with the Mitre his chance would be 1 - (0.9*0.5) = 55% (rather than 60%)
Eternal Hearts are a type of Heart introduced in Wrath of the Lamb. They act as a Half Red Heart until Isaac picks up a second one or moves onto the next floor (also works when the Forget Me Now is used), in which case it will turn into a filled Heart Container. Eternal Hearts alone are not enough to prevent death. If Isaac has an Eternal Heart but no Red Hearts, he will still die if he loses all of his Soul Hearts. However, the Eternal Heart will remain if Isaac comes back to life with Dead Cat, Ankh or 1UP.
Eternal Hearts can replace nonspecific Heart Drops with a 1/50 base chance or be granted by obtaining certain Collectable Items. They can also be found in the Cathedral-themed Super Secret Room. In addition, any nonspecific Hearts Spawned in that room will be Eternal.
It is possible to lose Eternal Hearts by getting hurt by enemies and Blood Donation Machines (including IV Bag). Blood Donation Machines take Eternal Hearts before any other type of hearts, but getting hurt by an enemy takes Soul Hearts first, then Eternal Hearts then Red Hearts. Unlike Soul Hearts, taking a full Heart of damage with just an Eternal Heart and Red Hearts will remove the Eternal Heart and half of a Red Heart, not just the Eternal Heart.
If you go into a Devil Room with no soul hearts and an Eternal Heart, and take a deal with the devil that doesn't kill you, you will lose the eternal heart. If Isaac goes into a Devil Room and he has an eternal heart and 2 or more soul hearts, and takes a deal costing two red hearts, Issac may die instantly.
Magneto will only attract Eternal Hearts when Isaac has unfilled Heart Containers.
If you obtain 7 or more total heart containers purely from eternal hearts in a single run (either from more to the next floor with an eternal heart or combining 2 eternal hearts) you will be given the achievement Eternal Life and be given flight for the rest of the run.
They act like Soul Hearts, meaning they disappear once a Black Heart container is depleted. When one of these hearts are depleted, though, they deal damage to all enemies and bosses in the room (In a fashion similar to the Necronomicon ).
Their priority on the Health Bar is the same as Soul Hearts. For example, if you've picked a Black Heart before a Soul Heart, the Soul Heart you'll have picked up will appear after the Black Heart on the health bar, meaning it will deplete itself before the Black Heart, and vice versa. Interestingly enough, picking up a Soul Heart when you have half of a Black Heart restores the heart entirely and gives half of a Soul Heart instead.
Picking up a Black Heart with a full health bar of 12 Hearts with at least one of these being a Soul Heart, the Black Heart will replace a Soul Heart.
Black hearts are also sometimes referred to as Revenge Hearts or Evil Hearts
These Hearts have a chance to be Red, Soul or Eternal.
- 1 — Completing rooms
- 1 — Poop
- 1 — Fires
- 1 — Keystones
- 1 — Champion enemies
- 1 — Slot Machines
- 1 — Portable Slot
- 1 — Beggars
- 1 — Bum Friend
- 1 — Justice Tarot Card
- 1 or 2 — Bosses (2 at the start, 1 when "Everything's Terrible" is unlocked. An extra Heart is gotten from Champion forms.)
- 2 — Shell Games
- 0, 1, or 2 — Chests
Items That Spawn Them
Items That Give Them
Items That Spawn Them
- 1 —Crystal Ball (May give a Tarot Card instead)
- 1 — Fortune Telling Machine
- 1 — The Relic
- 1 or 2 — Red Chests
- 1, 2, or 3 — Tinted Rocks
- 2 — The Hierophant Tarot Card
- 2 — Squeezy
Items That Give Them
- 1 — The Nail
- 1 — Book of Revelations
- 1 — The Mark
- 2 — The Pact
- 2 — Super Bandage
- 2 — Balls of Steel Pill
- 3 — Rosary
- 3 — Guppy's Paw (in exchange for 1 Heart Container)
- 1 — Shop
Items That Give Them
- 1 — Cathedral-themed Super Secret Room
"Maggy's Wig" - Have seven or more Heart Containers at once in a single playthrough.