You've heard of the Lifesaving Chain of Survival, or maybe you haven't - either way, you should know the links in the chain and the vital role of the bystander - a chain is only as strong as its weakest link, so don't be the weak link.
So what are the "links"?
EARLY ACCESS - this means getting the professional responders involved early in the process. After you have determined unresponsiveness in a suspected cardiovascular or cerebrovascular attack victim, Call 9-1-1. Also, retrieve an AED if you know one is nearby - you will likely need it. If you can, have someone else activate EMS (calling 9-1-1) and get the AED while you move on to other links in the chain.
EARLY CPR - Don't hesitate. CPR is not going to be effective unless started immediately - and don't worry about harming the victim.. many bystanders are concerned about tearing clothing, cracking ribs, or liability... The Good Samaritan Act is there to cover any liability, and damage to the victims clothing or ribs? Really? What could possibly be worse than death.. get started. Whether you know full CPR, or Compression only CPR - anything is better than nothing. If you are concerned about being "current" and knowing the latest CPR techniques, consider CPR Renewal now.
EARLY DEFIBRILLATION - Apply that AED and follow the directions. Any quality CPR course includes AED Principles, and you can get full AED certification with hands-on practice on an AED Trainer, too. Even if you have never had any training on AEDs, they are simple, and nearly all have both audio- and visual- guides to walk you through the process, including when to return to performing CPR... if your workplace, place of worship, or gathering spot doesn't have an AED - push for them to get one, or check out the AED Grant program.
EARLY ADVANCED CARE - Remember link one? Activating EMS? This is critical. You may have sustained the victim's viability/recoverability through CPR, you may even have resuscitated with you AED, but a person that has suffered such an event requires immediate advanced medical care... hand them over to EMS so they can stay alive and get what assistance they need to help avoid another life-threatening incident.