Stem Cell is an unlockable trinket in The Binding of Isaac, added in the Afterbirth+ DLC.

Traveling to a new floor heals 50% of Isaac's empty Red Heart and Bone Heart containers. Must heal a minimum of half a heart.

This page shows the latest information as of the new Repentance+ (Online Co-op) DLC.
To see information about this trinket for the previous Repentance version, check this page instead.

Defeat Ultra Greedier as Samson.

The following special synergies and interactions for Stem Cell have been documented.

* Note that not all possible synergies and interactions are listed here.

Below is the Internal Item Description as shown in-game.
Note that some stat changes are not displayed here. Please see the main description for the full effects.

Stem Cell

• Heals half of Isaac's empty red hearts when entering a new floor
• Golden Trinket (without Mom's Box): Heals all of Isaac's empty red hearts when entering a new floor
• Mom's Box: Heals all of Isaac's empty red hearts when entering a new floor
• Mom's Box + Golden Trinket: Heals all of Isaac's empty red hearts when entering a new floor

• Check out the trinket description on the external Isaac Wiki.