Melted Heart of Selig is a Unique Amulet. It can be used by any class.
The Melted Heart of Selig is a top-tier 
Mythic unique amulet in Diablo 4, offering substantial defensive and offensive benefits. It provides 30% to all resistances, increases the max resistance cap by 3%, and adds a 15% damage reduction while healthy.
Its standout feature is the 60 maximum resource boost, which not only increases your resource pool but also acts as a secondary health bar, absorbing 75% of incoming damage by draining your resource instead of HP. This makes it particularly valuable for builds that scale with maximum resource, such as Bone Spirit Necromancers or basic skill-focused characters.
Despite a recent nerf, it remains one of the most powerful and versatile Mythic uniques in the game, enhancing both survivability and damage output.
Effect
Damage is dealt to your Primary Resource before Life and damage taken this way is drastically reduced. Your Primary Resource is doubled but Maximum Life is reduced by 75%.
How to get Melted Heart of Selig
You can farm this unique from 
Duriel, Maggot King
Andariel, Maiden of Anguish
"Do not allow your passions to become obsessions. Fuel the fire that burns within you, but it is madness to allow yourself to become ash to please an uncaring universe." - Last words of Master Selig
Legions
Helltide