Two runners who died while participating in a 10-mile race in Herndon on Sunday suffered fatal heatstroke, according to preliminary autopsies performed by the Fairfax County medical examiner's office.

The runners, Patrick Reiley, 31, of Reston, and Henry J. Kronlage, 49, of Fairfax County, disappeared during the race on a day when area temperatures soared close to 90-degrees in the shade. Searchers found Reiley's body on Monday and Kronlage's on Tuesday.

With heatstroke, the body loses so much fluid that the victim can no longer sweat. This causes the body temperature to rise so high that organs are destroyed. Treatment for heatstroke is rapid cooling and fluids to be taken internally, authorities say.

The final autopsy reports will not be written until laboratory tests of the men's body tissue and fluids have been completed in a few weeks, according to Fairfax County police Sgt. Riley Wiley.

The deaths of Reiley and Kronlage bring to four the number of deaths known to have been directly caused by the high temperatures in the Washington area this summer, officials said.

On Monday 3-year-old Katrina Patrice Harrigan of Hyattsville died after being left inside a parked car in Falls Church. On Julu 21 a woman died at D.C. General Hospital after her body temperature rose to 108 degrees, a hospital spokesman said.

In addition, an unidentified youth in the Richmond area died earlier this week after suffering apparent heatstroke near a Henrico County school track, police said.