Obviously I did not examine his body (nor would I be qualified to do so), but a "heart attack" occurs when the myocardium (heart muscle) is not getting enough o

Obviously I did not examine his body (nor would I be qualified to do so), but a "heart attack" occurs when the myocardium (heart muscle) is not getting enough oxygen. The fight (brief as it was) ramped up his myocardial oxygen demand, and his position limited his body's ability to deliver that oxygen. That's a recipe for a heart attack. I should note that while "positional asphyxia" is a generally accepted theory, it's not without its detractors, and more research needs to be done. https://en.wikipedia.org/wiki/Positional_asphyxia https://en.wikipedia.org/wiki/Positional_asphyxia