For every 50,000 marathon runners, 1 dies of a heart attack within 24 hours of finishing the race!

This statistic applies to anyone who does strenuous activity for three or more hours. Researchers know that the reason is over-exertion of the heart muscle, which causes muscle cells to die. It's not an age thing either. According to their findings, younger, fitter people have a higher risk of having exertion related heart problems because they put more strain to their heart while exercising. Other facts about heart attacks:

• 39% of all heart attacks are fatal.
• About 57.5% of victims die before they are able to reach a hospital 
• Watching the World Cup increases the risk of a heart attack

To read more about the marathon runner statistic and the research behind it, click the source below!

(Source)