Final answer:
When a person is unresponsive and not breathing, after calling EMS, you should immediately begin CPR if you are trained, ensuring they are on stable ground if they were in water. Speed and the correct application of compressions can significantly improve their chances of recovery.
Step-by-step explanation:
After ensuring that an unresponsive and not breathing person has emergency medical services (EMS) on the way, you should begin CPR (cardiopulmonary resuscitation) immediately if you are trained to do so. It's critical to act swiftly to improve the person's chances of survival. If the person was in water, make sure they are on stable ground before starting CPR. While doing CPR, it is important to press hard and fast on the chest, at the rate of 100 to 120 compressions per minute and with a depth of about 2 inches in adult victims, to create the necessary gauge pressure to circulate the blood.
In the situation of a drowning victim, if the person is unconscious but has a sealed airway due to a muscular spasm of the larynx, they may still be able to be resuscitated effectively with CPR. Always keep in mind that a person can still be saved even if they appear unresponsive in the water, and that rapid initiation of CPR can increase their chances of survival significantly.