The man whose charred body was found on the grave of President Kennedy in Arlington National Cemetery last week died of heart disease, the authorities said today.

An autopsy determined that the man, Ramon Mejia, 44 years old, had a heart attack on the gravesite early on Nov. 28, Sandra Alley, a spokesman for the Federal Park Police, said.

The body was found about 8 A.M. by tourists, lying three feet from the eternal flame. Miss Alley said that Mr. Mejia had apparently been burned by the flame, but that the burns had not caused the death.