I get a little nervy when a cardiac event occurring on the football pitch makes international headlines, raising the question about cardiac risks in athletes. Here is an article in the BBC on the case of a recent English Premier League footballer who collapsed during a match.
Fortunately, sudden death in young athletes is a rare event. Most deaths in young athletes are not secondary to conventional coronary artery disease. Genetic abnormalities, such as hypertrophic cardiomyopathy, are usually associated with arrhythmias - irregular heart beats and sudden death. Having a genetic abnormality and playing a sport at a high level may increase the risk. These abnormalities may be difficult to detect, despite comprehensive testing.
For a more complete medical review on the matter, I defer you to this article, published in Current Opinion in Critical Care.
