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Melissa Ziebell was approaching the final mile of the 2015 Paris Half Marathon, her third ever, on track to break her personal best time of 1:45.

Then her legs seemed to seize up and stop working.

“I realized I was going to fall, and that’s the last thing I remember,” said the Colombian-born Ziebell, who was living in France at the time, working as an optical telecommunications researcher.

Only 33, she’d suffered a cardiac arrest, which occurs when the heart’s electrical system suddenly “short circuits” and the heart stops pumping. Each year, about 356,000 Americans suffer an out-of-hospital cardiac arrest, and the condition is fatal about 90 percent of the time.

Ziebell would likely have become just another unfortunate statistic were it not for the quick thinking of a pair of Red Cross volunteers stationed along the race route.

They started CPR and used an automated external defibrillator, or AED, to shock her heart with an electrical charge. That got it beating again.

Ziebell recalls awakening to the sound of someone calling her name and asking if she knew where she was.

“Kilometer 19,” she replied, rather than the more obvious “Paris, France.”

Then she tried to get up and start running again. After all, she’d been on pace to beat her personal best.

Fortunately, the medical volunteers were able to dissuade her of that idea and had her taken to a nearby hospital.

Melissa Ziebell at the starting line of the 2015 Paris Half Marathon. Her heart stopped a mile short of the finish line. (Photo courtesy of Melissa Ziebell)

Melissa Ziebell at the starting line of the 2015 Paris Half Marathon. Her heart stopped a mile short of the finish line. (Photo courtesy of Melissa Ziebell)

The cardiac arrest came as a complete surprise. After all, she was in extraordinarily good shape, working out for two to three hours a day, lifting weights and doing cardio, group exercises, kickboxing and roller blading.

Not to mention all the roadwork she did training for the half marathon.

Not only that, but before runners are even allowed to participate in the Paris event, they have to get a note from a cardiologist clearing them to run. Ziebell had gotten such a note.

In the hospital, her doctors determined she had an undiagnosed congenital heart defect. Given several treatment options, Ziebell chose to have the defect fixed because it carried the promise that she might be able to resume her rigorous physical activities.

Still, she was facing the prospect of open-heart surgery.

Melissa Ziebell (left) with her sister, Carolina, who flew to Paris after Melissa's cardiac arrest. (Photo courtesy of Melissa Ziebell)

Melissa Ziebell (left) with her sister, Carolina Ziebell, who flew to Paris after Melissa’s cardiac arrest. (Photo courtesy of Melissa Ziebell)

“I wasn’t surprised by her choice,” said her sister, Carolina Ziebell, who traveled to Paris to offer support. “She’s always been strong, independent and even stubborn that way.”

Following surgery, she was eventually released from the hospital and received a visa to travel to the United States, where she now works as a test engineer at Rockley Photonics in Pasadena, California.

“My health is good, I’m back to doing sports and, when the local American Heart Association chapter calls, I’ve done some speaking to the Latino community here in Southern California,” she said. “I talk about the importance of learning CPR because I wouldn’t be here today if those volunteers hadn’t given me CPR.”

She’s also training to run her first half marathon since her cardiac arrest. The race is in March.

This time, though, she’s not concerned about beating her previous personal best. Instead she’s looking forward only to finishing.

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