Explorer Sir Ranulph Fiennes is leaving for Kathmandu to embark on a 70-day trek up Mount Everest, in a bid to help children with heart disease.
The 61-year-old hopes to raise more than £2m for the British Heart Foundation charity.
Despite his wide-ranging expedition experience, Sir Ranulph is not an experienced mountaineer and admits to a fear of heights.
He has spent the past year preparing by scaling mountains around the globe.
Sir Ranulph is taking the more difficult northern route up the mountain.
Rock climbing lessons
The money he raises will help buy equipment for research into children with heart disease.
He has indicated the funds will go to a specific unit in the Great Ormond Street Children's Hospital, focusing on the growing amount of heart disease in six and seven-year-olds.
Sir Ranulph had a heart attack in 2003 followed by bypass surgery, but months later broke records by completing seven marathons on seven continents in seven days.
The explorer is famous for a three-year transglobe expedition and, along with Dr Mike Stroud, for attempts to reach the North Pole unaided and a 97-day trek across Antarctica.
Sir Ranulph began rock climbing lessons last summer with Haydn Griffith, a structural engineer from Cardiff.
Mr Griffith has helped Sir Ranulph scale rock faces at Avon Gorge, the Wye Valley, Taffs Well and the cliffs below Castell Coch in preparation for his Everest climb.
Sir Ranulph has also trained on Kilimanjaro, the Alps, and Cotopaxi volcano in Ecuador.