Published April 10, 2015 12:00AM

The Marathon des Sables is a six-day ultramarathon that stretches 155 miles through the Sahara in southern Morocco.
Endurance athlete Sir Ranulph Fiennes has complained of unnerving heart rhythms while competing in the Marathon des Sables, a 155-mile ultramarathon in the Sahara Desert, according to the Telegraph. His trainer, Rory Coleman, is urging Fiennes to be cautious.
“We need to be really careful,” Coleman told the Telegraph. “I don’t know if he is going to make it.”
Coleman’s concerns about Fiennes’ heart are not unfounded. The Berkshire-born former British Army officer has had two heart attacks and a double heart bypass in his lifetime.
Fiennes told Outside in March