This is what is supposed to happen if you develop sudden cardiac death during a marathon
More on the Detroit Marathon deaths.
The most likely natural explanation for the deaths is sudden cardiac death (an heart arrhythmia). This can be reversed by electrical depolarization of the heart, i.e. shocking him. You've seen it on TV a million times:
It is a pretty successful therapy. In fact, in the NY Marathon a guy collapsed at mile 19 and was saved by defibrillation. See here and here. He even has a twitter account. (Immediate follow)
I passed two of the resucitaiton efforts and they had defibrillators at the scene. This was no sudden cardiac death.