"I'm a school teacher. I don't like dropping out," said Joan Berman, 70, of Ann Arbor, Mich., who called it quits at the 8-mile mark. "But I know when to take a recess."
Berman has run 17 marathons, seven in Chicago, all since turning 60.

Death rate out of stroke or heart attack during marathons is high (1 out of 50k) and not only from the effort it takes.

NYT had an interesting article about it.

Thanks pitim for sharing
Chicago Marathon - Hot!
75 degrees and 86% humidity set the stage for the 30th Chicago Marathon.
http://www.marathonguide.com/index.cfm?

Is Marathoning Too Much of a Good Thing for Your Heart?

Race fields have grown. In 2005, 382,000 people completed a marathon in the United States, an increase of more than 80,000 since 2000, according to marathonguide.com. Meanwhile, the risk of dying from a heart attack during a marathon is about 1 in 50,000 runners, said Dr. Arthur Siegel, the director of internal medicine at McLean Hospital in Belmont, Mass., and an assistant professor of medicine at Harvard.
http://www.nytimes.com/2006/12/07/fashion/07Fitness.html?fta=y