It remains a difficult medical challenge to prevent the sudden cardiac death of athletes, typically defined as natural, unexpected death from cardiac arrest within one hour of the onset of collapse symptoms, excluding additional time on mechanical life support.[1] (Wider definitions of sudden death are also in use, but not usually applied to the athletic situation.) Most causes relate to congenital or acquired cardiovascular disease with no symptoms noted before the fatal event. The prevalence of any single, associated condition is low, probably less than 0.3% of the population in the athletes' age group,[citation needed] and the sensitivity and specificity of common screening tests leave much to be desired. The single most important predictor is fainting or near-fainting during exercise, which should require detailed explanation and investigation.[2] The victims include many well-known names, especially in professional association football, and close relatives are often at risk for similar cardiac problems.