Philadelphia (CBS) – Two male runners supposedly died of heart attacks while participating in the Philadelphia Marathon Sunday morning.

KYW’s Medical Editor Dr. Brian McDonough says in situations like this it is often difficult to predict who is going to be at risk.

“Obviously we would hope someone who is running in a race like this would have a physical examination and have a work up. Someone who is younger you start to think about a potential problem with the electrophysiology of the heart. Is there an irregular heart beat? Has the stress caused problems? Again we don’t know these things and sometimes physicians and pathologists never find out but clearly they’ll look into this and try to find out why these situations occurred. Certainly for the vast majority of people exercising and working out is a great thing but as you push it to greater levels there can be problems.”

Reported By Medical Editor Dr. Brian McDonough, KYW Newsradio