Cardiac Risk in Marathon Running: What the Actual Research Shows

Marathon cardiac events get outsized attention because they're rare and dramatic when they happen, which makes it easy to over- or under-estimate the actual risk. The largest study on record gives a real answer, and the most important finding in it isn't the headline risk number.

The scale of the study

That works out to roughly 1 cardiac arrest for every 167,000 finishers, across a dataset of over 29 million race results, the largest of its kind. 176 cardiac arrests were recorded in total over the 14-year study period: 127 in men, 19 in women, 30 where sex wasn't recorded. This is an extremely rare event at the population level, not a common risk any individual runner should expect to personally encounter.

The real finding isn't the risk rate, it's the survival rate

The incidence rate of cardiac arrest itself barely moved over the study period. What changed dramatically is what happens afterward: the case fatality rate, the share of cardiac arrests that end in death, fell from 71% in the 2000-2009 period to 34% in 2010-2023. Researchers attributed that improvement specifically to faster emergency response and better access to defibrillation on course. This is the actual headline: it's not that cardiac arrest has become rarer, it's that surviving one has become dramatically more likely, because of medical planning decisions race organisers actually control.

Who the data shows is at higher risk

Men face roughly 6 times the risk women do, and the full marathon distance carries roughly double the risk of a half marathon. Both patterns are consistent with what's known generally about exercise-related cardiac events: risk rises with exertion duration and intensity, and with age and sex-linked cardiovascular risk factors, not with something specific to the sport of running itself.