In reply to John Roberts (JR):
Interesting but it could happen to anyone, many hikers will put their heart under more duress than a fit fell runner, admittedly they often carry more kit.
I'd never take any kit on a standard fell run in the peak for up to a few hours. Of course things can and do go wrong, look at Bill Smith. could barely see, old man, running on his own.. I doubt he'd have wanted it any other way.. he loved the uncluttered freedom of running on the fells, even refusing to wear glasses yet had failing eye sight.
I know a lot consider it irresponsible but it's a principle attraction to the sport is running uncluttered and the risks involved. My favourite runs are always those squeezed in on the first night to a new area, often in the failing light, sometimes dark.. often no map, maybe one torch at most, often nothing, the day one of those goes wrong I'll be roundly criticised. But there's a feeling of total freedom and relief those runs give you.
