Many athletes, especially longtime, high-intensity endurance athletes, have heart-racing stories to tell—in more ways than one.

In 2009, Australian professional triathlete Erin Densham had to be rescued from the water during the Hy-Vee Triathlon in Des Moines, Iowa. Doctors diagnosed her with supraventricular tachycardia, or periodic rapid heartbeat. She had surgery to correct the condition and won bronze in the 2012 London Olympics.

American pro triathlete Justin Park was diagnosed in college with a congenital heart defect that causes heart palpitations and can lead to sudden cardiac death. He struggles with endocrine dysfunction and thyroid issues because of the condition, yet continues to regularly place in the top three in Ironman 70.3 events.


Photo by Bobby Ketchum, Flickr

If you experience an irregular or rapid heartbeat during training, racing, or even at rest, you may have some type of heart arrhythmia, or erratic heartbeat. Atrial fibrillation (AFib) is the most common type of arrhythmia. It happens when the heart’s upper chambers beat chaotically and out of sync with the lower chambers. Most of the time, AFib comes and goes. In some cases, it lingers for months or permanently.

AFib is one of a handful of common arrhythmias among athletes. Bradachardia, or low heart rate; sinus arrhythmia, where the heartbeat fluctuates with breathing; and premature ventricular contractions (PVC), or extra beats, pose no cause for concern. AFib, however, increases your risk for stroke (only slightly in healthy individuals). Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare, genetic heart disorder worth noting because it puts affected individuals at risk of sudden death, especially during heavy exercise.

Stronger hearts, higher risk

Older adults, heavy drinkers, and people with high blood pressure, underlying heart disease, and a family history of AFib have a higher likelihood of developing AFib. Oddly, so do the excessively fit. A 2013 study out of University Hospital in Bern, Switzerland reported a five-fold increased risk of AFib in middle-aged endurance athletes “with a striking male predominance.” (Women, take heart.)

Excess inflammation from training, nerve reflexes, a larger heart, and bradycardia are all proposed contributing factors to arrhythmias among endurance athletes, but true causes remain speculative. “We still don’t totally understand it,” says Michael Emery MD, a sports cardiologist and medical director for the Indiana University Health Center for Cardiovascular Care in Athletics.

It’s also unclear just how much exercise leads to increased arrhythmia risk. Will one marathon up your odds? Or does it take repeated Ironmans over decades? “Researchers are working to understand the mechanistic approach and what kind of lifetime ‘dose’ these athletes are exposing themselves to,” says Emery.

One thing is certain: the endurance athlete lifestyle—exercise, healthy eating habits, healthy weight and body fat—reduces the risk of heart disease, diabetes, and stroke. So while long-term endurance exercise may increase your risk of an arrhythmia, healthy habits reduce your risk of many other health conditions.

Will AFib end your athletic career, or worse? Probably not. “It’s usually not life-threatening because most athletes are so healthy,” says Emery. “It can be annoying; however, if it becomes disruptive to your lifestyle it could require a procedure or medication.”

If nerves cause your heart to race at the start line, don’t assume you have AFib. It’s difficult for even doctors to determine the difference between race jitters, starting too fast, and an arrhythmia.

One key sign, Emery says, is noticing your heartbeat. “Most people aren’t aware of their heart beating, even during exercise,” he says. “It may be nothing, but if you notice something unusual, it’s worth talking to your doctor about.” If you feel one little flutter, it’s probably okay to keep going. If you experience something more noticeable (see below), stop.

Park monitors his condition regularly, but hasn’t stopped racing. Most athletes with arrhythmias shouldn’t either. “If you want to lower your risk for heart disease and mortality,” Emery says, “lifelong endurance exercise offers the most bang for your buck.”

Arrhythmia warning signs

If you experience any of these symptoms while training or racing—stop. Doctor’s orders!

  • Irregular heartbeat
  • Unusual shortness of breath
  • Heart racing or skipping
  • Lightheadedness
  • Dizziness
  • Fainting
  • Chest pain or pressure (This is a medical emergency. Call 911.)

How to decrease your risk

Put less stress on your heart by maintaining a healthy lifestyle.

  • Limit caffeine and other stimulants (check your supplements for hidden sources).
  • Drink alcohol only in moderation. (You’re already doing this, right?)
  • Get adequate recovery. Overtraining stresses the heart in more ways than one.
  • Get enough sleep. Lack of sleep can precipitate some arrhythmias.
  • Reduce stress. Intense stress and anger up the odds for heart rhythm problems

Du It For  You note: A magazine editor assigned me this story. The magazine’s then-new editor-in-chief promptly killed it. Because I haven’t found a home for it yet, and because I think it’s worthwhile information for veteran endurance athletes, I’m publishing it here. If you’re an editor and interested in this story, get in touch!