Conrad Anker is arguably one of the world’s most accomplished climbers and continues to push himself. At 54, he has a track record of big sends and near misses on alpine peaks and big walls. He was recently in the Himalayas attempting the unclimbed 6,888-metre Lunag-Ri in Nepal with David Lama, 26. The pair tried the route last winter, watch a short film of their climb below.

On Nov. 16, Anker and Lama were six pitches up the line they attempted on their first trip. “It starts out with vertical ice and mixed climbing and hanging belays,” said Anker to Mark Synnott for National Geographic in an exclusive interview. “We were trying to move really fast on the first few pitches, because they’re in this funnel where you’re exposed to rock and icefall.”

As Anker was seconding a pitch in mid-morning, he felt something in his chest. After determining it wasn’t altitude sickness, he knew it was something bad and told Lama they had to descend.

Once the pair descended to advanced base camp, Lama organized a helicopter to get Anker to Siddhartha Hospital in Kathmandu. After some tests, the doctors determined Anker had a blockage of his left anterior descending aorta. “In medical terms they call it an acute cardiac syndrome, but for the layperson it was a heart attack,” said Anker. To read the full interview with Synnott see here.