Heartless

 is a perk in the Fallout: New Vegas add-on Old World Blues.

In the initial dialogue with Doctor Klein as part of the Welcome to the Big Empty quest, you find out that your brain, heart, and spine have been removed and replaced. This perk represents the replacement of your heart. While you technically have these perks from the start of the DLC, they are unlocked in the course of the conversation.

Effects
The description of the perk reads: "Your heart has been replaced with advanced technologies: You cannot be poisoned, and filters in your heart will also regulate bleeding and healing, allowing all healing items (chems) to function at a higher level. Robots are now confused by you and 50% less likely to score a critical hit."