AEDs won't shock a stopped ('flat line') heart back to like, like the 'paddles' on TV shows like '
ER'. They
may correct certain types of irregular heart rhythms, but won't do anything for other types of heart problems ('heart attacks').
http://en.wikipedia.org/wiki/Automated_external_defibrillator
They are one tool that is increasingly available outside of professional medical care (hospitals, paramedics, etc.). CPR is another technique that
may buy a victim time until they can get professional attention, with the more powerful drugs, tools, techniques, etc. It is something that you can try if you only have your hands, and some basic training. '
Compression only' training, in my understanding, has been promoted for people afraid of fluid contact with the victim, when performing the 'rescue breathing' part without a barrier mask or air bag. I don't know that it is 'better'.
Both of these are methods heavily based on the assumption that emergency assistance is nearby and available - e.g. an EMT response of 10 minutes or so in an urban area. In a remote situation, they may the only option to try.
I think that this is an important part of the training - letting lay rescuers understand that they are giving the victim a chance, but not guaranteeing survival. EMTs and paramedics may have access to additional options.
Philbert