In the initial dialogue with Dr. Klein as part of the quest Welcome to the Big Empty, the Courier finds out that their brain, heart and spine have been removed and replaced. This perk represents the replacement of their heart. While technically having these perks from the start of the add-on, they are unlocked in the course of the conversation.
Immunity to poisoning, adds a +25% bonus to healing items and -50% to Critical Chance for robots against the player character.
- Since the Cloud in the Sierra Madre is corrosive and not poisonous, it will still hurt the Courier even with this perk.
- Heartless shares the same Vault Boy image as Cardiac Arrest.
- Cazadores, usually being very lethal creatures, become significantly less threatening even in swarms due to their damage primarily relying on poison. This makes battles with the Legendary Cazador and the later encountered Specimen 73 much easier than normal.
Both Cardiac Arrest and Heartless do not affect healing from any items as they are missing the correct modifiers.