If Isaac has less than one full Red Heart after taking damage, he will be immediately teleported to the last cleared room he was in.
Quote
"Cursed?"
Effects
If Isaac has less than one full Red Heart after taking damage, he will be immediately teleported to a random room.
The teleportation happens only at half a heart or less left, regardless of health type. Empty Bone Hearts are not counted as health even if they can absorb a hit.