As a practicing EMT, I can assure you that the most important treatment in cardiac arrest is chest compressions. Properly done, they can keep blood circulating and greatly improve survival rates. Please take a CPR course. It is not difficult. If you took a course in the past and found the numbers confusing, do not worry, things are much simpler now. Compress, compress and compress. In the US, bystanders are protected from lawsuit in the event of negative outcome. The AED is helpful but properly done compressions will give the patient a chance while the AED is being located and put into service. By the way, in tests using properly trained fire fighters, it has been found that after two minutes of performing chest compressions fatigue sets in and the compressions become less effective. Thats why we line up behind the person performing compressions to take over at the two minute mark. Compressions must not be stopped during the changeover to the next rescuer.