A 73-year-old man collapsed and died while walking on the moors above Chorley.
The man had been with 10 companions from an organised walking group from Cheshire on Sunday.
The incident happened on Spitlers Edge, above Hordern Stoops, on the high point between Rivington and Belmont within the West Pennine Moors, in the afternoon.
Members of the walking group carried out continuous CPR on the man while they waited for the emergency services to arrive.
The Bolton Mountain Rescue Team, North West Air Ambulance, North West Ambulance Service, Lancashire Police and a United Utilities on duty local area patrol ranger attended the scene.
The air ambulance landed in very strong winds.
Bolton Mountain Rescue Team said its members, working in association with the NWAA air crew paramedic and doctor, took over the CPR, while drugs were also administered to the collapsed walker.
BMRT said despite the very best efforts of all on scene, the man had sadly died at the spot.
His companions were taken by two Lancashire Constabulary vehicles to their vehicles that were parked at Abbey Village.