That's what they taught us in Boy Scouts. Very first step is to get help.

Have someone call 911 (or whatever number in your country) immediately. If nobody is nearby start yelling.

Only one time in my life have I had to perform CPR (was already too late) but it is amazing how much of what I learned when I was 11 years old stuck with me.

Get help, check airway for obstructions...etc. Most importantly...take a CPR class sometime in your life and do what they say. The "ABC" of airway, breathing, circulation they taught us may not be current advice.

Sidenote: Don't be too hard on yourself if you don't save a life...even the pros say unless the patient is young/healthy you likely won't.

Edit: The feeling when the pros actually show up (in the case where I was doing CPR within minutes) is one of the biggest reliefs I have had in my life. Even knowing CPR...you feel helpless until they show up. And once they do, ask immediately if they need you. If not...get out of the way.

>The "ABC" of airway, breathing, circulation they taught us may not be current advice.

https://www.redcross.org/take-a-class/resources/articles/abc...

Some experts believe that some situations may see better outcomes if circulation is prioritized over respiration. Most experts agree that it is still best to teach ABC.

> The "ABC" of airway, breathing, circulation they taught us may not be current advice.

The version taught in Australian first aid classes is DRSABCD: check for (D)anger, check for patient (R)esponse, (S)end for help, (A)irway, (B)reathing, (C)irculation.