On November 16, Conrad Anker, 54, one of the world’s most accomplished alpinists, had a heart attack while climbing in the Himalaya. At the time he was clinging to a wall of ice and rock, just below 20,000 feet on the northwest face of 22,660-foot Lunag-Ri, with 26-year-old Austrian climber David Lama. It was the pair’s second attempt on the tallest unclimbed mountain in Nepal. (There are a couple higher unclimbed summits in Nepal, including Machhapuchhre at 22,942 feet, but they are considered sacred and closed to climbers.)

Most climbers his age are content to rest on their laurels, but Anker is an outlier, a man who has been pushing the cutting edge of alpinism for the past three decades. Four years ago, he summited Everest without supplemental oxygen as a member of a National Geographic expedition celebrating the 50th anniversary of the first American ascent. Anker and his teammates worked closely with the Mayo Clinic, whose doctors studied the climbers before, during, and after the expedition to learn more about the impacts of high-altitude climbing on the human body. Anker was the only team member to summit without supplemental oxygen, an effort, he admits, on which he may have pushed a touch too far.

“They did all these tests on me, and they said I tested like a person half my age,” said Anker. “But I definitely cooked a few brain cells, and it felt like I had weakened my heart, like I charley-horsed it or something.”

It has been a particularly challenging year for Anker, who in April helped recover the body of his best friend and climbing partner Alex Lowe, who was lost in 1999 in an avalanche, along with fellow climber David Bridges, on Mount Shishapangma in Tibet. Anker was caught in the same avalanche but miraculously survived. In the aftermath of the tragedy 16 years ago, Anker and Lowe’s widow, Jenni, fell in love and married, and Anker has helped raise Lowe’s three sons.

National Geographic reached Anker via Skype, shortly after he returned to his home in Bozeman, Montana. Sitting at his desk, with a framed photo of Yosemite Valley in the background, Anker spoke candidly about the incident that nearly cost him his life.

What happened?

I was six pitches up the route that David and I attempted last season. It starts out with vertical ice and mixed climbing and hanging belays. 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. At about 9:30 a.m., I was seconding [following] with a pack on, and I felt tired and out of breath. Initially I thought, The sun will come, I'll warm up, I'll feel good, and then we'll finish the next two pitches to get to our bivouac site. Then all of a sudden it was like, Bam, what the heck is that? It wasn’t bubbly lungs or my head feeling spacey. Altitude sickness comes on slowly; this was sudden. I later learned I suffered an acute thrombotic occlusion of the approximal LAD artery. In medical terms they call it an acute cardiac syndrome, but for the layperson it was a heart attack. When I got to the belay, which was the first one where you could actually sit down, I said “David, this is not good."

How did you get down?

David led the rappels down. As we hiked down through the icefall I realized that I had a numb lip and pain in my left arm. Every time you go into the doctor's office they always have these charts: How to recognize a heart attack, how to recognize stroke, how to perform the Heimlich maneuver. You're not committing them to memory, but with repeated exposure you understand them, so that was sort of how I self-diagnosed.

How did David cope with the emergency?

He was just so focused and caring and knew exactly what was going on. When we got to Advanced Base Camp, we met up with Tensing and Martin, two of our staff, and I said, "Yeah, I got this. I'm just going to heal up." David said, "Hey, this is serious. You need to go out now. Don’t think you can just work through the pain. You need to get a helicopter." David arranged for that right away. It took a while for it to show up. That whole time I was breathing through the pain. I took an aspirin as a blood thinner, but I couldn't keep it down.

Who organized the rescue?

I told David he needed to call Global Rescue, but we didn’t have their number because it was in my wallet down at base camp. [Editor’s note: Global Rescue provides rescue insurance for all members of the American Alpine Club.] So David called our outfitter, who figured out that a helicopter operated by Manang Air was in the area. They picked up Lakpa, who runs air traffic control at Everest Base Camp. It was lucky because he’s a Sherpa and he knew right where we were. He’s also a friend; he’s been to Montana to visit. We flew to Lukla and they took me off and said, "Can you just sit for a bit?" I didn't protest, but inside I’m thinking, Well, yeah, but I’m kind of hurting. While they loaded up rice, a microwave, and some other crap, I'm sitting in this little shed, sheet white, breathing through severe pain.

They finally got me to Siddhartha Hospital in Kathmandu. It’s the ex-pat hospital, started by David Shlim. It’s a reputable hospital, and the cardiologist that I worked with was trained in the U.S. The first thing they did was put me on an EKG, which showed an abnormality, then they did an angiogram. They put an iodine-based dye in your blood system and then x-ray your chest. It showed a major blockage. They were planning to just assess the problem and then do something about it the next day, but it was so serious that they said I needed angioplasty right away. They told me there's a one percent chance there could be a complication and a .01 percent chance that the complication could lead to fatality. I had no choice, so I told them to take care of it.

Were you awake for the procedure?

Yeah, they went in through my arm. I could feel it tickling around in there. My arm is still tender. It feels like it got run over by a mountain bike. The tool they use is like a micro-[auger] with a J-hook at the end. The doctor worked it up through my arteries, and every time he came to a fork he knew where to go. He got to the blockage and then pulled the plaque out. They showed it to me. Imagine a little piece of a broken-up peanut. It's that color, but it was fatty tissue. Next they inserted a balloon with a stent inside. The relief was instant.

I’ve always wondered what would happen if you got sick in a foreign country. Do they take insurance?

"We don't take Blue Cross,” they said. “Are you willing to pay for all this?" They got my passport, and they had my credit card. They wanted me to pay for a nurse, but I just had one of my Sherpa buddies come and stay with me. He slept in the room and brought me tea and took care of me. I was in the hospital for two nights. A bunch of kind people came to visit me, bringing flowers and whatnot.

How did you get home?

VF was super-helpful. [Editor’s note: "VF" stands for VF Corp, the corporation that owns The North Face. Anker is a founding member and captain of The North Face Athlete Team.] They flew Jenni over, and then we both flew back to the States, business class. It was the first time I’ve ever flown business class overseas, and it was incredible. My seat fully reclined into a bed, which is exactly what I needed. We landed in Chicago, and then the VF airplane took us to Rochester, Minnesota, where the Mayo Clinic is located. We stayed in a hotel there for three days while they did more tests on me. My cholesterol is fine. My lipids are fine. My enzymes are fine. The ability for the heart to pump is strong. My valves are good. I had some weakening of tissue, but no necrosis, so that was a key thing. I did a stress test, and even after the heart attack they told me I'm still healthier than most men my age.

Were they able to figure out how or why this happened to you?

I’ve been working with Dr. [Bruce] Johnson for the past five years as part of a study looking at the effects of climbing at high altitude on the human body. It’s kind of a mystery where this came from. There's no history of heart disease in my family. My grandparents all lived into their late eighties, early nineties. My dad lived to 84. My mother is 85. I think a lot of it is stress. I have thick blood with a high hematocrit level and a high red blood cell count. I always take aspirin prophylactically when I’m climbing at altitude, but somehow I forgot this time. I wasn't going that high so I didn’t think I needed it. I was able to acclimatize quickly and everything was ready to go, but I was climbing with three layers of long underwear, carrying a pack, and it was minus 20 [degrees]. The hanging belays [in which you sit in your harness without a foot stance] probably affected the femoral artery and how it circulates blood to my legs.

Are you going to change your lifestyle as a result of this?

Yeah. When I look at red meat now, it's totally different. We brought a ton of meat up there, little pork chops and bacon. I've always seen the iron and protein as a benefit to climbing at altitudes. I never eat the fat off pork chops, but on this trip we were chewing on it. It's supercold, so you want to make sure that you stay warm, and you get that out of fat. I'll have fish a couple nights a week and poultry one night a week. I haven’t had any alcohol since this happened, but the Mayo Clinic said I could have a glass of red wine. I need to reduce the amount of stress in my life. There's work stress, but my domestic life is stressful, too—being where I am for the last 16 years, how Jenni and I got together, and all that.

How do you get rid of that type of stress?

Meditation. Mindfulness. Learning to identify situations that create internal stress and trying to minimize them. Figuring out what's important in life. It's easy when you're climbing, because you're like, OK, I'll put a piece of gear in. I can process the fear and channel it in the right direction. But in everyday life it’s a lot harder.

Do you think you will continue to climb first ascents in the Himalaya?

This was a clarion call. Do I still need to be doing stuff like Meru [the Indian Himalayan peak that is one of Anker’s most famous and daring summits, featured in a 2015 film]? I don’t necessarily need to be out there pushing it. There’s plenty of other things to do. Jenni is happy for that. I did think to myself, Oh, I won't have a job, so maybe I'll become a school bus driver until I can find something else. But The North Face said, "No, you're still OK. Don't worry about it." I want to be graceful about how I taper things down.

What are some projects outside of climbing you’re working on?

I started working with the Mayo Clinic back in 2012 when we did the Everest trip, and I’d like to keep building on that relationship. Mayo Clinic does a lot of testing for wearable devices, and I’d like to see these devices work on health prevention. The data can be used to identify children at risk for type 2 diabetes. We’re working in conjunction with Kaiser Permanente, an insurance company based out of the Bay area, that’s on the leading edge of preventative health care. We want to work with school teachers and primary care doctors to identify kids who are at risk and then get them into climbing gyms.

Is there any silver lining to this happening when it did?

I've always tried to live a selfless life, to dedicate my life to others, like I've done with Alex's boys and Jenni and with the Sherpa community. Then it was my turn. Karma came around. I think about what if this happened in June when I was in Tibet to get Alex’s body. We were at the same elevation [19,350 feet], and I rappelled with him off an ice cliff, down through an icefall, and then eight miles back to base camp.

You carried him out?

Yeah, he probably weighed a hundred pounds. It was brutal. The whole day I probably drank one Coke and ate nothing. I went through Advanced Base Camp, where we’d been camping, and I found an old tent pole from our expedition. Going back up there and seeing everything was super-emotional. I was stressed, and I felt my heart. I had to process the whole survivor’s guilt thing all over again. That day started at 3 a.m., and I got back to base just as the sun was setting. Jenni was waiting for me. If it had happened then in Tibet, realistically it could have been four days before I could have gotten to a Chinese hospital. Had it happened there it would've been really traumatic for Jenni and the family. The irony and the karma of it all would've been just absolutely crushing. Afterward it was definitely a full PTSD type of thing. I saw something that I never …

What happens next?