Diagnosed at 10 months old with a bicuspid aortic valve — a heart condition in which the aortic valve has two leaflets instead of the normal three, causing unusual strain to the heart — Kantner grew up with restrictions on the type of activities in which he could take part.
“I played hockey in Michigan until it became only a contact sport, which I couldn't play,” says Kantner, 38, who now lives in Erie, Colorado. “I never played football, and I didn't really care for sports like baseball and soccer. So in college I got into weight training, abiding by my restrictions.”
In 2025, Kantner found a new fitness obsession — Hyrox, a competitive indoor sport in which participants alternate between running and completing fitness stations such as a weighted sled push and burpee broad jumps. At his third official competition in February 2026, Kantner finished in the top 20% of contestants.
“I’ve always liked being competitive — I don't know if that has to do with the fact that I'm like, ‘Hey, I can do this better, even with a deficient heart,’” he says. “They hold Hyrox events all over the world, and my wife and I have started using them as a reason to go on a trip.”
As Kantner’s passion for Hyrox grew, so did the complications associated with his bicuspid valve. He had received annual heart checkups his whole life, and in 2024, his cardiologist told him the calcification of his valves was getting worse and his aorta was beginning to stretch.
“Prior to that, it was always, ‘moderate to severe stenosis, but nothing requiring intervention yet,’” Kantner says. “But in 2024, he said, ‘It's getting to the point where we can see some progression,’ meaning the calcification of the valve and the size of the aorta getting larger.”
As an engineer who manages projects for BAE Systems (previously Ball Aerospace), Kantner approaches everything in his life from an analytical standpoint. When he first met with T. Brett Reece, professor of cardiothoracic surgery in the University of Colorado Anschutz Department of Surgery, he had a lot of questions about the valve replacement surgery he would need to repair the bicuspid valve.
“I’m a 38-year-old competitive male athlete. I couldn’t find a lot of information on the internet about what to expect and how to choose a valve, and then what does recovery look like?” he says.
Reece talked Kantner through his options — either a mechanical valve, which is more durable but requires the recipient to take blood thinners the rest of their life, or a biological valve, made from human or animal tissue, which could wear out faster than a mechanical valve.
“There's a huge push against mechanical valves in our community right now,” Reece says. “Nobody wants to take a blood thinner, and that's why it's pushed against. But I feel like the pendulum swung so far away from this type of valve that we're probably too far. Many people would get a huge benefit from a mechanical valve, and we have a couple of studies now that show patients under 60 may live longer if they have a mechanical valve. It's certainly an option that is worthwhile for many patients.”
Kantner opted for the mechanical valve, deciding that being on blood thinners was worth it for a new valve that will likely last the rest of his life.
“I had some conversations with Reece about, ‘If I went mechanical or if I went tissue, are either of those going to have limitations on the type of strength training and cardio training that I enjoy doing?’” Kantner recalls. “He said, ‘No, they're both fine. Just know that a biological valve is going to have to be redone every 10 years.’”
Kantner underwent the open-heart operation in March 2026; in addition to the valve replacement, Reece repaired his aortic aneurysm. After seven days in the hospital, Kantner returned home and began walking every day as part of his recovery. Six weeks later he started running three times a week, and 60 days after his surgery, he ran the Bolder Boulder 10K. He chronicled his progress on Instagram.
“He wanted to make sure that young people knew that you can get a mechanical valve, which is probably the most durable thing that we have in terms of the aortic valve replacement, and still live your life, still be active, still be athletic, and live the life that you want,” Reece says.
As he continued running and training for his next Hyrox event in November 2026, Kantner discovered an unexpected benefit of his valve replacement — because his body had gotten used to the limitations of his bicuspid valve, the repair meant he could exercise harder than ever before.
“It was around three months post-surgery when I realized, ‘Hey, it's kind of easy to do a 26-minute 5K now. Maybe I have a little bit more capacity from the oxygenated blood that is no longer regurgitated,’” he says. “I've got more plumbing capacity than most because of the way that the heart grew because of the deficiency. It’s good to be on the other side of recovery.”