PHILADELPHIA (CBS) – Sudden cardiac arrest is normally associated with middle aged or older individuals, but younger people can experience it as well, often without warning. Fran Crippen (in photo above), a swimmer from Conshocken, Pa. died after his heart stopped during the Swimming World Cup in the United Arab Emirates.

A Heart Walk in Philadelphia November 13th is taking place to raise money and awareness.

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Thomas Jefferson University Hospital cardiologist Dr. Arnold Greenspon says cardiac arrest can occur without warning due to a life threatening arrythmia, ventricular fibrillation which can be corrected with a shock from an AED or defebrillator:

“People who are fit have a lower incidence of sudden death, but yet even fit people are highest risk for heart problems at peak exercise.”

The water Crippen was swimming in was 84 degrees. The race winner,  Thomas Lurz of Germany, said that’s too hot to race and the schedule was too grueling. Dr. Greenspan says this just goes to show that we need to monitor ourselves during strenuous physical activity:

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“We need more information. But, think about it. Any type of extreme sport, the body is really under tremendous stress. Imagine if somebody was swimming and the water temperature was high.”

Possibly altering the body’s core temperature and metabolism, leading to cardiac arrest but Greenspon says we may never know.

Main Line personal trainer Mark Peters was just 22-years-old and training a client in the gym when he suffered sudden cardiac arrest:

“My heart completely stopped. I was revived about two minutes later with a defibrillator.”

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Reported by Michelle Durham, KYW Newsradio