Mr. Nutrax collapsed right in front of me from sudden cardiac arrest. (This was a different episode from the one I mentioned in the blood thread where his life was saved by donated blood). The first thing I did was call 911, as had been drummed into me in my emergency response class. I was still assessing whether or not Mr. Nutrax was breathing when the fire department arrived (the station is very close.) They had him under CPR for almost 20 minutes before they were able to get his heart started again, using a defibrillator.
That was three years ago. He's still very much alive, although recovery was a long haul, due to some brain damage.
I got the names of all the firefighters & paramedics who showed up and sent them an effusive thank you letter, that started out "you saved a life last Saturday..." That made their day--they rarely hear about the outcome of a medical call.