The results showed that during a marathon, over half of the segments of the heart lose function, Larose said. The reason turns out to be an increase in inflammation and a decrease in blood flow through the muscle. -msnbc.msn.com
MY COMMENT: They also noted the fitter you are, the less the damage. Dehydration was associated with greater damage. Deaths during marathons are extremely rare, especially in the absence of atherosclerosis, however as the author notes "People should not enter a marathon lightly. Training needs to be well done… You can't cheat the marathon."