Heart

The small heart is an item obtained from bosses and enemies in the bloodmoon. When picked up they dont stay in ur inventory but immidiatly give u a 20 health regen. The bloodmoon is a good tactic for fighting a boss because of the 10% droprate that zombies and even slimes and eye balls drop. Hearts dont count against item health regen and so dont give a overall cooldown. They are not yet able to go in the inventory for save-up.