Having worked in a medical environment before coming in to aviation (and a little bit during my flight training) and having read this thread with interest I will say that the reply immediately prior to mine, by dubbleyew eight hits the nail on the head. The chap in question appears to have suffered a myocardial infarction [edit: actually I should say probably has suffered an MI]
Blood has a propensity to clot particularly when not flowing correctly. A heart condition itself may cause that - such as atrial fibrillation - and an AF patient knows, or should know, he or she is more at risk of stroke, for example, as the irregular rhythm can "throw up" clots. AF of course would (or at least should) be detected or indicated by ECG and then other verifications.
The other reasons for an obstruction are, as dubbleyew eight has said, attributed to factors which reduce or impede blood flow - long period of inactivity being one, narrowing arteries another. Some people have a natural or inherited tendency to what is sometimes called "sticky" blood and as such are placed on blood thinning medication such as warfarin or heparin (other blood thinning drugs are available).
For the heart to arrest then there is almost always and external reason for it doing so. Hearts rarely just stop on their own, although it is not impossible and there is usually an external cause. Heart failure as a condition is different to a heart attack. A patient can live with heart failure as it is a progressive condition. I have seen drug abusers, trauma (accident) patients amongst other suffer cardiac arrest with an otherwise healthy heart.
Finally, there are factors that can be assessed and tests that can performed to indicate your "risk" of suffering a cardiac event including an myocardial infarction and hereditary factors are important too.
And whilst there is much talk here about BMI and keeping fit - all crucial to maintaining good health - there will continue to be otherwise supremely fit people who ace their medicals but then drop a medical time bomb and stun us all.
Disclaimer from me: I do not offer the above text as any form of official or unofficial advice. You should always speak with your treating clinician and if you suffer any of the conditions I refer to above you should discuss the implications with them.
Last edited by StatorVane; 30th Sep 2013 at 06:51.