The good news is that the short answer is no! But only if you are using a Public Access Defibrillator (PAD) which is always of the Automated External Defibrillator (AED) type and not the clinical type you would see on Holby City and similar TV programs (or in a hospital, obviously).
AED's are wonderful tools, available in a growing number of settings, for use by the general public in the event of a suspected Cardiac Arrest. Indeed, in a pre-hospital environment, if an AED is used on a casualty who is suffering a cardiac arrest within the first 3 minutes after the arrest, it will increase their chances of survival by up to 72%! That is opposed to the chance of surviving being 10% if you receive CPR alone.
An AED will carry out a test of the casualty before it decides whether or not they require a shock and will not release the shock until it is satisfied in a number of areas. How big the casualty is, whether the casualty is moving and whether the casualty's heart is in a shockable rhythm. That's right, an AED will not shock someone if their heart has completely stopped, it will merely request that a rescuer carry out CPR. An AED is only useful to a casualty who's heart is in a fibrillating (quivering) rhythm and will deliver the shock to stop the heart, in a similar way that you may turn off a computer that is in an error state.
I will explain the use of AED's in following blogs.