Is there also a big difference between giving CRP to someone who has drowned & someone who has had electrical shock or heart attack etc - My understanding from Diving first aid is that in the case of drowning, CPR is more likely to be effective because its probably not a faulty heart that's the primary problem, whereas most other causes are due to disruption of the hearts rhythm being the primary (by which I mean "electrically" or muscular rather than lack of oxygen!), in which case CPR doesn't work as well as "resetting" the heart with an AED.