Periapt of Wound Closure

From Dungeon Master's Guide, page 184. Found on Magic Item Table F.

Description
''Wondrous item, uncommon (requires attunement). 1 lbs.''

While you wear this pendant, you stabilize whenever you are dying at the start of your turn. In addition, whenever you roll a hit die to regain hit points, double the number of hit points it restores.