Sir Ranulph has taken medical advice

The adventurer, who lives on Exmoor on the Somerset-Devon border, is to run seven marathons on seven continents in seven days to raise money for the British Heart Foundation.

The charity challenge will take place between October 26 and November 2.

Sir Ranulph, who is 59, had an emergency by-pass operation at Bristol Royal Infirmary in June after being taken ill at the city's airport.

Sir Ranulph has a history of doing things against the odds James Andrew, sponsor

He will be accompanied on the marathons by his long-time adventure companion Dr Mike Stroud and support vehicles will carry a defibrillator in case he has any heart problems.

The first marathon will be on King George Island, Antarctica's northernmost tip, on 26 October.

From there, the pair face a gruelling schedule of long-haul flights and runs in Santiago, Sydney, Singapore, London and Cairo, before finishing in New York on November 2.

James Andrew, a spokesman for Land Rover, which is sponsoring the 7x7x7 Challenge, said Sir Ranulph had taken medical advice and was now in training.

He had decided to take it on as a tribute to the treatment and support he had received following his heart attack.

Polar exploration

Mr Andrew said: "This challenge has been on his mind for a while, but his heart attack was the motivating factor.

"He knows himself better than anybody. He has taken medical advice and feels he can do it, so why shouldn't he? After all, he has a history of doing things against the odds."

Sir Ranulph has been awarded the OBE for "human endeavour and charitable services", received a double clasp to his Polar Medal for outstanding achievements in polar exploration, as holds Sultan of Oman's Bravery Medal.

In 1982, a transglobal expedition led by Sir Ranulph was the first successful circumnavigation of the globe on its polar axis.

In 1993, Sir Ranulph became one of the first men to walk unaided across Antarctica.