Defibrillator

The 'Defibrillator, also referred by survivors as "chest paddles", is an item used only in Left 4 Dead 2, symbolized by a lightning bolt. It can be used to revive dead teammate and can only be used once. For balancing purposes, the player can not carry a defibrillator and health pack at the same time.

To use the defibrillator, players must walk up to a corpse, which will acquire a faint red glow, and press mouse1 / right trigger. A charging meter, which takes 5 seconds to complete, is shown. Then, there is a short burst of electricity and the teammate has been successfully revived. He/she comes back at 50 health (which is permanent health that doesn't drop like temporary health gained when being revived after being incapacitated) and can pick up all dropped items before continuing. There will be a message on the left side of the screen informing everyone who brought whom back to life. The Defibrillator can become especially useful in Expert difficulty and/or Realism Mode, where a Witch is able to instantly kill a player.

The defibrillator in action here, 6:00-6:10.