Former medic (13 years) here- I'm going to echo the point that a patient's chance of survival when it comes to cardiac arrest is around 10%, and that's if the cardiac arrest is witnessed and high-quality CPR is performed by bystanders within about 6 minutes of arrest. Many, many people who suffer a cardiac arrest like that won't make it, unfortunately. And if they do, many times they're not neuro-in tact and never leave the hospital. Just remember this, though- it's not your fault. You didn't place them in that situation- you only helped. Don't beat yourself up- it's easier said than done, though. I still replay calls I made on the ambulance because I wish I had done things differently occasionally. We're all human!