Athlete’s Heart: Symptoms, Causes & When to Worry

Athlete’s Heart: Symptoms, Causes & When to Worry

Athlete’s heart is the normal way the heart adapts to years of intense training. A well-trained athlete’s heart is often larger, beats more slowly at rest and pumps more blood with each beat. These changes are a sign of fitness, not disease.

However, some of these normal changes can look like serious heart conditions on an ECG or echocardiogram. And rarely, a dangerous heart problem can hide behind what looks like athlete’s heart. Here’s what’s normal, what causes these changes, and when an athlete should see a cardiologist.

What Is Athlete’s Heart?

Athlete’s heart, also called athletic heart syndrome, describes structural and electrical changes in the heart caused by regular, intense exercise. It’s most common in people who train many hours a week, such as competitive endurance athletes, team-sport athletes and dedicated recreational athletes.

Athlete’s heart is not a disease and doesn’t need treatment. In most cases, the changes partly reverse within a few months after an athlete reduces training.

What Causes Athlete’s Heart?

During exercise, the heart pumps up to five or more times as much blood as it does at rest. Over time, it remodels to handle that workload more efficiently. The type of training shapes how the heart adapts:

  • Endurance training (running, cycling, swimming, rowing) mainly increases the size of the heart’s chambers, so each beat moves more blood.
  • Strength training (weightlifting, wrestling, throwing sports) mainly thickens the heart’s walls to handle short bursts of high pressure.
  • Mixed sports such as basketball, hockey and soccer often produce a combination of both.

A larger, more efficient heart can move the same amount of blood with fewer beats. That’s why many athletes have a resting heart rate in the 40s or even lower.

Common Signs of Athlete’s Heart

Athlete’s heart usually causes no symptoms. It’s often noticed during a physical, a pre-participation screening or a test done for another reason. Normal findings include:

  • A slow resting heart rate (sinus bradycardia), sometimes below 50 beats per minute
  • A heart murmur caused by increased blood flow, often harmless
  • An enlarged heart on an echocardiogram or chest X-ray, with normal pumping function
  • Mildly thickened heart walls
  • ECG changes that would be unusual in non-athletes but are considered normal in trained athletes

Expert guidelines, known as the International Criteria for ECG interpretation in athletes, list ECG findings that are normal in athletes. These include a slow heart rate, mild heart block (first-degree AV block), early repolarization and high voltage suggesting a larger heart. Recognizing these patterns prevents athletes from being wrongly disqualified from sport.

What Makes the 'Athlete's Heart' So Unique? | by Brady Holmer | Sharing Science | Medium

Athlete’s Heart vs. Hypertrophic Cardiomyopathy and Other Conditions

The biggest challenge is telling athlete’s heart apart from heart conditions that can cause sudden cardiac arrest during exercise. The most important is hypertrophic cardiomyopathy (HCM), an inherited thickening of the heart muscle. We cover HCM in more detail in 5 lesser-known heart conditions.

Other conditions that can mimic or hide behind athlete’s heart include:

  • Arrhythmogenic cardiomyopathy (ARVC), in which heart muscle is replaced by scar and fat
  • Dilated cardiomyopathy, a weakened, enlarged heart
  • Myocarditis, inflammation of the heart muscle, often after a viral illness
  • Coronary artery anomalies, arteries that start or run in an abnormal location
  • Inherited rhythm disorders, such as long QT syndrome, Brugada syndrome and Wolff-Parkinson-White syndrome

In athletes over 35, coronary artery disease becomes the most common cause of exercise-related cardiac events. The ACC summarizes the causes of sudden cardiac arrest and death in athletes.

When to Worry: Warning Signs in Athletes

Athlete’s heart itself doesn’t cause symptoms. If an athlete has any of the following, they should stop training and see a cardiologist:

  • Fainting or near-fainting during or right after exercise. This is the most important red flag.
  • Chest pain or pressure with exertion
  • Shortness of breath out of proportion to the effort
  • Palpitations, a racing or irregular heartbeat, especially with dizziness
  • A sudden drop in performance or unusual fatigue without explanation
  • Symptoms after a viral illness, such as chest pain or palpitations after COVID-19 or the flu
  • A family history of sudden cardiac death before age 50, cardiomyopathy or inherited rhythm disorders
  • An abnormal ECG flagged during a screening physical

Long-term endurance athletes, especially middle-aged men, also have a higher risk of atrial fibrillation, an irregular heart rhythm. The ACC reviews what contributes to AFib in former endurance athletes. For a broader checklist of symptoms, see 10 warning signs you should see a cardiologist.

Call 911 if an athlete collapses. Start CPR and use an AED immediately. Every minute without CPR and defibrillation lowers the chance of survival.

How Doctors Diagnose Athlete’s Heart

A cardiologist experienced with athletes uses several tools to separate normal adaptation from disease:

  • 12-lead ECG, interpreted using athlete-specific criteria
  • Echocardiogram to measure wall thickness, chamber size, pumping and filling
  • Cardiac MRI to look for scarring or abnormal thickening patterns, especially in gray-zone cases
  • Cardiopulmonary exercise testing to measure fitness and check rhythm during exercise
  • Holter or event monitoring to record the heart’s rhythm over days to weeks
  • Genetic testing when an inherited condition is suspected
  • Supervised detraining, a short period of reduced exercise, followed by repeat imaging

The goal is to keep healthy athletes in their sport while protecting those with a real risk. Today, many athletes with a heart condition can continue to compete after an individualized, shared decision-making discussion with their cardiologist.

Heart Screening for Athletes

In the U.S., pre-participation physicals typically include a medical history, family history, and physical exam. Some programs, including many collegiate and professional leagues, also add an ECG and echocardiogram. Beginning in the 2026-2027 school year, under Florida’s Second Chance Act (Florida Statute 1006.20), students participating in any Florida High School Athletic Association (FHSAA)-sanctioned athletic tryout, conditioning, practice, or competition for the first time must have a cleared electrocardiogram (ECG/EKG) before they can participate.

Read the American Heart Association’s overview of screening young athletes for heart disease.

Adult and masters athletes, especially those over 35 or with risk factors such as high blood pressure, high cholesterol, diabetes or smoking, may benefit from a cardiology evaluation before starting or intensifying training.

Frequently Asked Questions

Is athlete’s heart dangerous? No. Athlete’s heart is a normal, healthy adaptation to training. The concern is making sure it isn’t hiding a different heart condition, which a cardiologist experienced with athletes can sort out.

Is a resting heart rate in the 40s normal for athletes? Yes. Trained athletes often have resting heart rates in the 40s and sometimes lower. A slow heart rate is a concern only if it comes with dizziness, fainting, fatigue or shortness of breath.

Does athlete’s heart go away? The changes usually partly reverse within a few months of reducing training. This is one way doctors distinguish athlete’s heart from conditions like hypertrophic cardiomyopathy, which don’t improve with rest.

Can you have athlete’s heart without being a professional athlete? Yes. Marathon runners, triathletes, cyclists and other dedicated recreational athletes who train many hours a week can develop athlete’s heart.

Should my child get an ECG before playing sports? It depends on your child’s history, symptoms, family history and sport. A doctor can review whether an ECG is appropriate. Any child who faints during exercise, has chest pain with exertion or has a family history of sudden cardiac death should see a cardiologist before playing.

Sports Cardiology Care in Tampa

As team cardiologist for the Tampa Bay Lightning and former team cardiologist for the Toronto Raptors, our cardiologist has evaluated elite athletes at the highest level of competition. We bring the same expertise to athletes of every age and level, from high school competitors to weekend warriors and masters athletes.

We offer athlete-specific ECG interpretation, echocardiography, exercise testing and individualized return-to-play guidance.

Request an appointment or call (813) 540-4322.

602 S Audubon Ave, Suite A, Tampa, FL 33609

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