Cardiopulmonary resuscitation (CPR) is a lifesaving technique useful in many emergencies, including a heart attack or near drowning, in which someone’s breathing or heartbeat has stopped.
CPR can keep oxygenated blood flowing to the brain and other vital organs until more definitive medical treatment can restore a normal heart rhythm.
When the heart stops, the lack of oxygenated blood can cause brain damage in only a few minutes. A person may die within eight to 10 minutes.
If you are untrained and have immediate access to a phone, call your local emergency number before beginning CPR. The dispatcher can instruct you in the proper procedures until help arrives.

*https://www.mayoclinic.org/first-aid/first-aid-cpr/basics/art-20056600 as accessed on 18 Aug 2020