The following items are designed to augment your team’s general health. They are carried on your back, and you can carry either the Defibrillator or the First Aid Kit, but not both.
Either of these items are carried when selected, and a Melee Shove can be used to push a foe back before you use the item. (Using Melee Weapons is better, though, because the foe will simply return to attack after a Shove). You have no other offensive capabilities while you’re holding either the Defibrillator or the First Aid Kit.
Defibrillator
Encountered infrequently and easily distinguishable, Defibrillators offer the user the chance to save the life of a downed teammate if they have already succumbed to their wounds, but before they are transported to a Rescue Closet. Get to them during the minute or so that their corpse is lying on the ground.
Administer the Defibrillator as you would any other item and requesting cover from remaining teammates so you aren’t attacked during the resuscitation. When complete, the victim is revived, although they still may need additional healing.
The Defibrillator isn’t usually picked up in favor of First Aid, due to the (understandably) selfish nature of Survivors. However, if you usually take a long-range view of combat, you might carry this device to use on an aggressive teammate who gets into a situation they can’t resolve with blind, ugly violence.
Try grabbing these to use during a finale or other major occurrence where you know there’s likely to be Health already available, such as the finale at the Tank eatery during Hard Rain.
First Aid Kit
First Aid Kits are found dotted randomly through a location, although the number lessens on more difficult game settings. The Kits are always found inside Safe Rooms, and usually found in First Aid Stations.
When you administer the First Aid Kit, you are prone and almost immobile (you can turn, and fire at incoming foes when being healed by someone else, but should not move, or the administering begins again) for around 4 seconds, so request cover from a teammate. First Aid can be given to a wounded teammate (who can provide the cover for you).
Around 60 points of the Health you have lost is restored when you use a First Aid Kit, up to a maximum of nearly 100 Health. This means you receive much more Health if your Health is closer to zero than 100, so judge the optimal time to use it.
As you begin to slow down at around 50 Health or less, this is the time to administer First Aid, but try to survive a little longer if additional Kits are not available.