The total number of hearts the player has. Two Health means two heart containers, and so on. Note: The only exception for this rule at the moment is ???, who has -1 health. This means he has Soul Hearts instead of normal ones.
The health stat cannot exceed 12 hearts. Soul Hearts do not share this limit.
If Isaac's health surpasses 12 hearts, he will not gain any additional hearts, but Guppy's Paw will be able to use those excessive health stat values to gain further soul hearts. Deals with the Devil can also utilize an excessive health stat.
Should Isaac's health go below 12 heart containers again, the excessive health will be changed into empty heart containers, until the full amount of health (12 containers) is reached again.
If you gain an empty heart (Health Up pill, Odd Mushroom (Large) or Holy Grail) while your red hearts are reduced to zero, the game will also give you a half heart to prevent you from dying.
Each Heart Container holds one full heart of HP, taking damage will empty one half or one full heart container.
The maximum number of heart containers can be increased by consuming an HP up item or pill, up to a maximum of 12. Any heart containers found past that point can be spent at Devil Room, but not filled with hearts or half-hearts.
Empty heart containers can be filled using hearts or half-hearts.
Heart containers can be spent like currency in the Devil Room and can be emptied for cash at a Blood Donation Machine.
??? cannot have any heart containers.
===Health Up Items===
A number of treasures in game will increase your number of heart containers. Numbers in parentheses indicate how much health it heals. Items with an asterisk are only available in Wrath of the Lamb. These items give soul hearts when playing as ???.
Number in braces denotes the amount of health healed on pickup.
+1 heart container
* Dessert (1)
*Rotten Meat (1)
*Blood Bag (5) (Also increases Speed by 0.3)
*The Halo (1) (Also increases Speed by 0.3, Tears by 0.2, Health by 1, Damage by 0.3, and Range by 2.75)
*Magic Mushroom (1) (Also increases Range by 7.75, Speed by 0.3, Damage by 0.3, and multiplies damage by 1.5)
*Odd Mushroom (Large) (0) (Also increases Damage by 0.3, Range by 2.75 and reduces Speed by 0.1)
*Super Bandage (1) (Also adds 2 Soul Hearts)
*Stem Cells* (1.5) (Also increases Shot Speed by 16%)
*Stigmata* (0) (Also increases Damage by 0.3)
*MEAT!* (1) (Also increases Damage by 0.3)
*Holy Grail* (1) (Also gives flying)
*SMB Super Fan!* (1) (Also increases Tears by 0.2, Damage by 0.3, decreases Speed by 0.2)
*Health Up Pill (0)
*Strength Tarot Card (Temporary) (1)
*Eternal heart* (1) (delayed, see below)
*Possible effect from Liberty Cap* (Temporary) (0) (can copy Odd Mushroom for one room)