CPR for heart attack victims started in less than about 2 min. is 20% effective. In the state of WA where they are ahead of the edge in training everyday people in CPR it's about 33%. I think the last time I took my CPR training (about 2 mos ago) the figure for trauma (car accidents) was less than 7%. If you are not a first responder than these figure may seem pesimistic, but if you can give someone even a 1% chance of living for a few minutes of your time than I hope it would be worth the try.