A 22-year-old runner who was taken ill after completing the London Marathon died today, race organisers said.
The marathon's organisers said the runner died peacefully this morning, and offered their "deepest sympathy and condolences" to his family and friends.
A spokeswoman for the organisers said a second runner, who had been in a critical condition in hospital last night, was better today and had been transferred to a normal ward.
Sweltering heat left scores of contestants needing medical treatment. Temperatures hit just below 21 degrees at midday, almost equalling the 1996 record, and rose slightly higher later in the day.
Runners reported "nightmare" conditions, and ambulance staff said they dealt with a higher than usual number of patients.
A spokeswoman said some people were suffering heat-related problems such as dehydration as well as sprains and other injuries.
A London marathon spokeswoman said 57 people were taken to hospital, and the St John Ambulance service said it treated 5,032 people.