A London Ambulance Service spokesperson said: "We were called just before 8.45am to reports of a passenger taken unwell on a flight from New York to Kuwait.
"The aircraft was diverted to Heathrow and we sent an ambulance crew and a cycle responder. We treated one woman and took her to Hillingdon hospital."
The woman's illness was not confirmed but the spokesperson said she "became unwell" during the flight, which had been due to land in Kuwait City at 9.25pm (BST) tonight.
A spokesperson for Heathrow Airport said: "KU118 from JFK to Kuwait was diverted to Heathrow after a passenger was taken ill on-board.
"The passenger was looked after London Ambulance Service and the flight is resuming its journey shortly."
The diversion came the day after Isis bombed a Shia mosque in the country, killing at least 27 people on Friday.
Several people with alleged links to the suicide bomber have since been arrested.
British tourists were among dozens of people shot dead by an Isis militant on a beach in Tunisia yesterday and a man was also beheaded in France on the day becoming known as 'Bloody Friday'.
- Independent