> I can't accept that this guy really was in perfect health;
I guess that depends on why you mean by 'perfect health.' He may very well have been in perfect health by every outward appearance. There are a large number of surprisingly minor things that can make you dead in an instant.
A brief primer on electrocardiology... Each heart beat is divided into several phases. An electrical impulse in generated in the two small chambers at the top of the heart (the atria), causing them to contract. This is the first small bump in an EKG, and is called the 'P' wave. After a brief pause, the impulse is conducted to the big chambers at the bottom of heart (the ventricles), causing them to contract. This is the big wave on an EKG, called the 'QRS complex.' After that, there's a period of time where the cells in the ventricles are recharging. This is the final bump in the EKG, called the T wave.
The Wikipedia article on this topic is very good. http://en.wikipedia.org/wiki/Electrocardiography#Waves_and_i...
If the heart is shocked (physically or electrically) during that recovery period, it can throw the heart into a fatal dysrhythmia where all the muscle cells in the heart are contracting chaotically. This is what happens when a baseball, lacrosse, or hockey player takes a blow to the chest and goes into sudden cardiac arrest... The blow happened during that very narrow window or time.
It's possible for your own heart to do that to itself though... It's very common for healthy people to have occasional 'premature ventricular contractions' where some random cell in the heart decides it's pissed off and wants to contract early. These are generally harmless, and happen all the time without anyone noticing. Every once in a while though, one of those PVCs occurs during that recharging phase, which can be very bad... So, a 'perfectly' healthy person _can_ throw a PVC, end up with an R-on-T contraction, and whamo... they're dead. Is it common? No, it's extremely rare. Does it happen? Sure does...