Your legs feel like lead ― if you can feel them at all. Every step forward requires gargantuan effort. Sweat stings your eyes. Despite the burn you can see the finish line and you will yourself to push on. Now is not the time for your heart, of all things, to give out.

The tragedy of having a heart attack in the middle of a marathon has attracted attention in recent years after some unfortunate deaths in the United States. But marathoners, take heart: The chance your heart will give way at the halfway mark of your next twenty-six-point-two is relatively low.

A new ten-year study published in the New England Journal of Medicine found that the majority of those who suffered a heart attack during marathons and half-marathons had preexisting undiagnosed heart abnormalities, such as thickening of the heart muscle or coronary artery disease. More than 85 percent of those experiencing a heart attack were men, and their risk rose over time. The average age was 42, and heart attack was most likely to hit during the last quarter of the race.

But the mortality rate among marathoners was only 71 percent, much better than the 92 percent of people suffering a heart attack outside of a hospital. The researchers noted this was probably thanks to spectators giving CPR and on-site medical personnel.

Past studies have also found that running marathons doesn’t damage the heart, a concern among some in both the running and medical communities. But the research stresses that it’s important to make sure your heart is healthy before you run. And having folks trained in CPR nearby during the race is crucial, too.

So before you sign up for a marathon, schedule a visit with your doc first to make sure your ticker can go the distance. A willing mind is nothing without a healthy heart.