Veteran explorer Sir Ranulph Fiennes is receiving medical attention at the  Marathon des Sables after running for 30 hours in temperatures topping 50C. Sir Ranulph, 71, completed the most gruelling stage of the desert race today, but was taken straight to the medical tent because the exertion had begun to take its toll on his heart. He was forced to lie down intermittently during the last few hours of the run because of fears he would not be able to finish the stage and described the experience as 'more hellish than hell'. Medical attention: Sir Ranulph Fiennes, 71, was taken to the medical tent because of concerns for his heart . Heath: The explorer previously suffered two heart attacks and underwent a double heart bypass, a cancer operation and is in an ongoing fight with diabetes . Gruelling: He ran for 30 hours in heat topping 50C through the desert, but had to lie down intermittently to continue . He previously suffered two heart attacks and has undergone a double heart bypass, a cancer operation, and is in an ongoing fight with diabetes. Speaking from the medical tent, Sir Ranulph said: 'I became woozy and had the feeling I was going to faint. It's not worth pushing it when you get that. 'My trainer Rory had to push me down to the ground to rest and then pick me up again every so often, that is how we made the last 5k.' He added: 'Last night was pretty horrific, it's hell on earth. You're trying to go up hills and your feet are slipping backwards in the sand. 'I had some really shaky moments. My head-torch faded and I couldn't see the hills. But Sir Ranulph, in a bid to become the oldest Briton to complete the six-day ultra-marathon in the South Moroccan desert, said thoughts of the Marie Curie teams he is raising money for kept him going. Finish line: The race is not over and he still has one more marathon to complete tomorrow before finally finishing . He said the work of Marie Curie Cancer Care nurses, who are also working through the night, keep him going . 'More hellish than hell': The 71-year-old explorer said he became 'woozy' and thought he was going to faint . Sir Ranulph is pictured here with his trainer Rory Coleman who pushed him down to the ground to rest before picking him back up again . He said: 'What kept me going was the thought that Marie Curie nurses are also working through the night. 'This is all to raise funds for the amazing care they provide to people who are terminally ill and their families.' Sir Ranulph, who began the challenging fourth stage of the event on Wednesday morning, has covered 56 miles, stopping for only an hour at 4.30am this morning to sleep out on the course. But the race, which has already seen more than 75 people drop out, is still not over and he still has one more marathon to complete tomorrow before finally finishing. To support Sir Ranulph and donate to Marie Curie Cancer Care, visit www.justgiving.com/ranulph. Tough: 75 people have dropped out of the six-day Marathon des Sables which pushes runners to their limit . Sir Ranulph gets ready to set off on his fourth day (left) and pictured right on the final stretch of the fifth day . There were fears he would not finish this stage of the race, but he was helped by his trainer Rory Coleman .
Sir Ranulph Fiennes is receiving medical attention at Marathon des Sables .
Veteran explorer, 71, has completed most gruelling stage of the desert race .
Forced to lie down intermittently during last few hours so he could finish .
Aiming to become the oldest Briton to complete the six-day ultra-marathon .