From Dark and Darker Wiki

Utility Data is currently up to date for: Patch:6.7#Hotfix 74

Soul Heart.png
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Move Speed -10
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Glowing blue soul heart of a fallen adventurer.
Use at an Altar of Sacrifice to resurrect your teammate by sacrificing -20% of your current health. 
Type:
SoulHeart
2x2InvSlot.jpg
Stack Size:
1
Gear Score:
0
Sell Price:
5
Glowing blue soul heart of a fallen adventurer.

Utility

Utilities are single or multiple-use items that can be used during combat or to complete a variety of tasks.

Description

To resurrect an ally you will need to locate their Soul Heart which is located in their chest armor slot. To acquire their heart you will need to remove their chest armor piece. Equip their soul heart to you utility bar then proceed to look for an Altar of Sacrifice. After locating a Altar of Sacrifice, hold your team mates soul heart in your hand and press interact button. This initiate a channel action that will resurrect your team mate when the bar is full. Being hit or moved will cancel this action. You can't take enemy's soul hearth.