The medical examiner's office says hyperthermia caused the Brooklyn man's death on Friday.
The National Weather Service says the air temperature reached 96 degrees in the city that day.
The man's name wasn't released, and details on the circumstances of his death weren't immediately available.
It was at least the second heat-related death in the city this month.
The medical examiners' office found a 57-year-old Staten Island man died of hyperthermia on July 8, when the temperature in the city reached 89 degrees.