A person who is unresponsive is not breathing or has no pulse and cannot respond to you when you shake them or ask if they are okay. If you see this, call 911 and search for the nearest CPR-savvy passerby to assist until paramedics arrive.
If an adult is unresponsive and not breathing, they require high quality CPR. High quality CPR involves chest compressions and rescue breaths following the recommended guidelines and techniques. It also includes calling for help and using an AED (described below).
The first thing to do is make sure the scene is safe. Check for a pulse by looking for a rise and fall of the victim's chest, which can be seen if they are lying on their back on a hard surface. You may also feel for a heart rate in the neck by sliding fingers into the groove between the stenocleidomastoid muscle and the trachea and feeling for a pulse with 2-3 fingers. The rate should be greater than 60 beats per minute and be felt within 10 seconds.
If no pulse is found, begin with 30 chest compressions minimum 2 inches deep. After each chest compression, check for a pulse with 2-3 fingers, checking for the presence of a rhythm that is faster than 60 beats per minute. If a heart rhythm is detected, continue with rescue breaths every 2 or 3 seconds (20 to 30 breaths per minute). Continually assess for normal breathing and the presence of a pulse until EMS providers take over.