Cardiac Arrest/Old World Blues

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

Requirements
Convince your brain to return to your body or convince it to come back to The Sink. After, you can have your heart reinserted into your body.

Effects
You gain +50% poison resistance, +50% bonus to healing items and robots have -50% critical chance against you. Compared to the Heartless perk, you gain an additional +25% bonus to healing items at the cost of 50% poison resistance rather than immunity. Grants the full 85% resistance to poison when combined with 8 Endurance, the maximum you can achieve in derived statistics.

Bugs

 * This perk grants -50% critical chance from enemy robots, rather than the listed -25%. For PC users, a fix for this perk along with Brainless and Big Brained is available here.

Behind the scenes
Apparently, the original counterpart to Heartless was to be called 'Heart-full', and the description implies it would have provided +5 Barter, +5 Speech, and an additional 10% chance to hit enemy torsos in VATS. Additionally, there is also a mirror of Cardiac Arrest with a different description and the effects from Heartless.