Frostbite occurs when the body's tissues freeze deeply in the cold.18 Ice crystals that form in the tissues cause damage to the cells. This is the opposite of a burn, but it does almost identical damage to the skin.
Treating frostbite19 is a delicate procedure of gradual warming. If at all possible, this should be done by professionals at a medical facility. First, get out of the cold. Small areas of minor frostbite20 may be rewarmed by skin-to-skin contact, but avoid using any heat sources or hot packs.
If you can't make it to a medical facility, use immersion of the affected area in warm water (98 to 105 F) for 20 to 30 minutes to rewarm it. Do not rub the affected area or use heat sources.

Cardiopulmonary resuscitation (CPR) is the most important medical procedure of all.2 If a person is in cardiac arrest (the heart is no longer pumping blood) and CPR is not performed, that person will die. On the other hand, performing CPR or using an automated external defibrillator (AED) could save a life.3
You can start by reviewing the basics of CPR. The procedure has changed in the past few years, so it is best to take a CPR class at a medical center, community college, Red Cross, or fire department. There is no substitute for a hands-on class.
AEDs are available in many public areas and businesses.4 These devices are simplified for use even if you have never been trained. CPR training will include familiarization with AED use.
According to the American Heart Association and American Red Cross 2015 guidelines, the steps to take when a cardiac arrest5 is suspected are:
Command someone to call 911 or the medical alert system for the locale.
Immediately start chest compressions regardless of your training. Compress hard and fast in the center of the chest, allowing recoil between compressions. Hand this task over to those who are trained if and when they arrive.
If you are trained, use chest compressions and rescue breathing.
 An AED should be applied and used. But it is essential not to delay chest compressions, so finding one should be commanded to someone else while you are doing chest compressions.

 
Basic First Aid for Bleeding