When a runner's heart stops during a marathon, it gets a lot of press — even though it's actually a pretty rare event. A more common killer among runners, and a condition that needs more prevention efforts, is heatstroke, according to a study by Israeli researchers.

During a 2011 running race, physicians at a Tel Aviv hospital noticed there were far more heatstroke victims admitted than . They wondered if this was an anomaly, so they analyzed local races from March 2007 to November 2013, encompassing 137,580 runners.

Across those races, there were two serious cardiac events, neither of which was fatal or life threatening. But there were 21 serious heatstroke cases, including two fatalities and 12 that were life threatening.

There's a continuum of , ranging from milder heat cramps all the way to heatstroke, which is defined as a fever above 104 degrees and symptoms including dry, hot skin, rapid breathing and unconsciousness. When the body gets that hot, the kidneys, brain and other organs can fail.