Is Running Bad for Your Heart? What the Research Really Says About Endurance Exercise and Heart Health

Running is supposed to be good for your heart.

But spend enough time reading headlines about marathoners, ultrarunners, and lifelong endurance athletes and you might start wondering if the opposite is true.

Can running cause atrial fibrillation? What about coronary artery calcification? Does years of marathon and ultramarathon training eventually damage the heart?

These aren't completely unreasonable questions.

Over the past decade, researchers have discovered something interesting. While runners generally have excellent cardiovascular health and lower rates of cardiovascular death, some lifelong endurance athletes also appear to have higher rates of certain cardiovascular abnormalities.

That sounds contradictory.

It isn't necessarily.

The evidence suggests that running is overwhelmingly good for your cardiovascular system, but decades of very high volume endurance training may come with some unique cardiovascular considerations.

Let's look at what we actually know.

TLDR: Is Running Bad for Your Heart?

For the overwhelming majority of people, running is one of the best things you can do for cardiovascular health. The interesting question is what happens at the extreme end of the spectrum after decades of high volume endurance training.

Here are the main points:

• Runners have a substantially lower risk of cardiovascular death than nonrunners.
• Even relatively small amounts of running appear to provide meaningful cardiovascular benefits.
• Lifelong endurance athletes can develop normal structural changes known collectively as the athlete's heart.
• Long term, high volume endurance exercise has been associated with a higher risk of atrial fibrillation, particularly in male endurance athletes.
• Some older lifelong endurance athletes have surprisingly high levels of coronary artery calcium and coronary plaque despite otherwise excellent cardiovascular fitness.
• Athletes tend to have more heavily calcified plaque, which may be more stable than softer plaque, but researchers still don't know exactly what that means for long term cardiovascular risk.
• Small areas of myocardial fibrosis, or heart tissue scarring, have also been observed in some veteran endurance athletes.
• These findings do not currently outweigh the well established cardiovascular and longevity benefits of exercise.
• The smartest approach for lifelong runners is not to stop running. It is to train while still paying attention to blood pressure, cholesterol, family history, symptoms, recovery, and other cardiovascular risk factors.

In other words, running isn't bad for your heart.

But running 50 to 100 miles per week for 30 years isn't necessarily the same physiological exposure as jogging three miles a few times per week.

That distinction matters.

Running Is Very Good for Your Heart

Let's start with what we know with the greatest confidence.

Physical activity dramatically improves cardiovascular health.

Running can improve cardiorespiratory fitness, blood pressure, insulin sensitivity, body composition, endothelial function, and numerous other factors associated with cardiovascular disease.

More importantly, runners tend to live longer.

One of the most frequently cited studies followed more than 55,000 adults for approximately 15 years.

Compared with nonrunners, runners had approximately:

30% lower risk of death from any cause

and

45% lower risk of cardiovascular death.

Even more interesting, people didn't have to run huge mileage to see benefits.

Running as little as 5 to 10 minutes per day at speeds below six miles per hour was associated with lower mortality risk compared with not running.

A larger systematic review and meta analysis involving more than 232,000 participants reached a similar conclusion.

Compared with people who did not run, runners had approximately:

27% lower risk of all cause mortality

30% lower cardiovascular mortality

and

23% lower cancer mortality.

So if the question is simply:

Is running healthy for your heart?

The answer is pretty clearly yes.

But that's not where the debate gets interesting.

What Happens When You Run for Decades?

Most exercise recommendations are based on moderate amounts of physical activity.

A lifelong endurance athlete may accumulate something entirely different.

Consider someone who runs 50 miles per week.

That's roughly:

2,600 miles per year.

26,000 miles per decade.

And potentially more than 75,000 miles over 30 years.

During much of that exercise, cardiac output increases dramatically. Heart rate remains elevated for hours. Blood flow through the coronary arteries increases. The chambers of the heart experience repeated volume and pressure loads.

The heart adapts to this stress.

Most of those adaptations are beneficial.

But researchers are increasingly asking whether decades of extremely high endurance exercise could also produce some unwanted adaptations in susceptible individuals.

A recent joint consensus statement from experts associated with the European Association of Preventive Cardiology and American College of Cardiology acknowledges exactly this issue. While exercise improves cardiovascular health and reduces cardiovascular events and mortality, masters athletes may have higher rates of certain abnormalities, including atrial arrhythmias, coronary atherosclerosis, myocardial fibrosis, and other cardiovascular changes.

That doesn't mean endurance exercise is unhealthy.

It means the relationship between exercise and heart health may become more complicated at the extreme end.

The Athlete's Heart Isn't Necessarily a Damaged Heart

Endurance training causes the heart to remodel.

The heart may become larger.

The left ventricular chamber can increase in size.

The right ventricle can adapt.

Resting heart rate frequently decreases.

Stroke volume increases.

These changes allow the heart to pump large amounts of blood efficiently during exercise.

Collectively, these adaptations are often referred to as the athlete's heart.

Most of this remodeling is considered physiological rather than pathological.

In other words:

A different looking heart does not automatically mean an unhealthy heart.

This is an important distinction because endurance athletes can sometimes have ECG, echocardiogram, or imaging findings that would look unusual in a sedentary person.

The more interesting question is whether some adaptations eventually cross from beneficial remodeling into potentially harmful remodeling.

That's where atrial fibrillation enters the conversation.

Running and Atrial Fibrillation

One of the more consistent cardiovascular concerns associated with long term endurance exercise is atrial fibrillation, commonly called AFib.

AFib is an abnormal heart rhythm originating in the upper chambers of the heart.

Interestingly, moderate exercise appears to reduce the risk of AFib.

But extremely high levels of endurance exercise may increase it in some populations.

This is one reason researchers sometimes describe the relationship between exercise and certain cardiovascular outcomes as U shaped or J shaped.

Being sedentary is bad.

Moderate exercise is very good.

Large amounts of exercise are still associated with substantial health benefits, but certain risks may begin increasing again at extremely high training volumes.

Potential explanations include repeated stretching of the atria, enlargement of the atrial chambers, changes in autonomic nervous system activity, inflammation, and possible fibrosis.

This phenomenon appears particularly relevant to middle aged and older male endurance athletes with long histories of training. Reviews of masters athletes continue to identify atrial fibrillation as one of the more important potential consequences of decades of intensive endurance training.

That doesn't mean every ultrarunner is eventually going to develop AFib.

Far from it.

But it is a legitimate association worth understanding.

The Really Strange Finding: Coronary Artery Calcium

This is probably the most fascinating part of the endurance exercise and heart debate.

You would expect lifelong endurance athletes to have pristine coronary arteries.

Many do.

But not all of them.

Several studies have found unexpectedly high levels of coronary artery calcium, or CAC, in some veteran endurance athletes.

Coronary calcium is generally considered a marker of coronary atherosclerosis.

Normally, more coronary calcium means greater cardiovascular risk.

That makes the findings in endurance athletes surprising.

A recent systematic review examining coronary artery disease in masters athletes identified coronary calcium and coronary plaque in a meaningful proportion of athletes despite their high levels of physical activity.

A 2025 systematic review and meta analysis examining extreme endurance athletes also found athletes were more likely to have coronary atherosclerosis compared with controls.

But there was an important catch.

The athletes were not more likely to have high risk or obstructive plaques.

And that distinction may be extremely important.

Could Runners Have More Plaque but Safer Plaque?

Not all coronary plaque is identical.

Plaque can broadly contain varying amounts of:

Calcified material.

Fibrous tissue.

Lipids.

Different plaque compositions carry different risks.

Soft, lipid rich plaques can be particularly concerning because they may be more likely to rupture and trigger a heart attack.

Interestingly, some studies of endurance athletes have found that their coronary plaques tend to be more heavily calcified.

One hypothesis is that exercise could potentially promote plaque stabilization or calcification.

In other words, an endurance athlete could theoretically have a higher coronary calcium score while having plaque that is relatively stable.

That would create a strange situation where an athlete's CAC score looks concerning while their actual cardiovascular risk may not be equivalent to a sedentary person with the same score.

But this remains an active area of research.

Recent reviews emphasize that endurance athletes can also have mixed and noncalcified plaque, meaning we shouldn't simply assume that all plaque in athletes is harmless.

This is one of the biggest unanswered questions in sports cardiology.

Does Running Actually Cause Coronary Calcium?

We don't know.

That's important.

Association does not prove causation.

Someone who has spent 30 years running marathons has also spent 30 years aging.

Diet matters.

Genetics matter.

Blood pressure matters.

LDL cholesterol matters.

Smoking history matters.

Family history matters.

Stress matters.

Researchers have proposed several mechanisms through which decades of extreme endurance exercise could potentially influence coronary calcification, including repeated increases in coronary blood flow, vascular shear stress, inflammation, calcium metabolism, and mechanical stress on the arterial wall.

A 2025 review in Circulation Research noted a consistent signal of increased coronary artery calcification particularly among older men with very high lifetime endurance exercise exposure.

But the authors also emphasized that we still don't fully understand the clinical consequences.

That's a recurring theme with this research.

We are getting better at finding abnormalities.

We don't always know what those abnormalities mean.

What About Scarring of the Heart?

Another controversial finding involves myocardial fibrosis.

Fibrosis essentially means small areas of scar tissue within the heart muscle.

Cardiac MRI studies have detected fibrosis in some lifelong endurance athletes.

One theory involves repeated episodes of extreme cardiac stress.

During prolonged endurance exercise, particularly events lasting many hours, the right ventricle experiences substantial workload.

The heart normally recovers.

But researchers have proposed that repeated exposure over decades could potentially lead to small areas of fibrosis in susceptible athletes.

Once again, this doesn't appear to happen to everyone.

And we still don't know exactly how clinically important small amounts of fibrosis are in otherwise healthy athletes.

Current reviews nevertheless identify myocardial fibrosis as one of the potential cardiovascular changes observed more frequently in some middle aged and older endurance athletes.

What About Heart Attacks During Marathons?

Whenever someone suffers cardiac arrest during a marathon or running race, it understandably attracts attention.

But the important distinction is that exercise can temporarily trigger a cardiac event in someone who already has an underlying cardiovascular problem.

That is different from saying running caused the underlying disease.

Vigorous exercise temporarily increases cardiovascular stress.

Heart rate increases.

Blood pressure increases.

Cardiac output increases dramatically.

Catecholamines increase.

For someone with significant coronary artery disease or an undiagnosed cardiac condition, that increased demand can potentially trigger an event.

The American Heart Association has emphasized that vigorous exercise can temporarily increase the risk of sudden cardiac death or myocardial infarction in susceptible individuals, particularly people who are unaccustomed to strenuous exercise.

At the same time, habitual exercise dramatically lowers cardiovascular risk over the long term.

That's an important distinction.

Exercise can temporarily increase risk while you're exercising while simultaneously reducing your overall lifetime risk.

Is There Such a Thing as Too Much Running?

Possibly.

But science hasn't identified a mileage number where running suddenly changes from healthy to unhealthy.

There isn't evidence showing that:

40 miles per week is safe.

But 41 miles is dangerous.

Biology doesn't work that way.

Lifetime exercise exposure probably interacts with numerous factors, including:

• Genetics
• Age
• Sex
• Training intensity
• Recovery
• Blood pressure
• Cholesterol
• Diet
• Previous cardiovascular disease
• Smoking history
• Family history

Two runners could train identically for 30 years and experience completely different cardiovascular outcomes.

This is why the question shouldn't necessarily be:

"How many miles are too many?"

A better question might be:

"How is my cardiovascular system responding to the amount of training I'm doing?"

Should Marathoners and Ultrarunners Be Worried?

I wouldn't stop running because of this research.

The overall evidence simply doesn't support that conclusion.

Running remains strongly associated with lower cardiovascular mortality and longer life expectancy.

But I also wouldn't use fitness as proof that you're immune to cardiovascular disease.

This is where endurance athletes sometimes make a mistake.

You can run a three hour marathon and still have high LDL cholesterol.

You can finish a 100 mile ultramarathon and still have hypertension.

You can have an extremely high VO2 max and still have coronary plaque.

Fitness does not make you bulletproof.

A 2025 meta analysis found that endurance athletes had more coronary atherosclerosis than controls even though they did not have more high risk or obstructive plaque.

That should reinforce something runners sometimes don't want to hear:

You still need to pay attention to the boring stuff.

Blood pressure.

Cholesterol.

Blood sugar.

Family history.

Diet.

Sleep.

Recovery.

And symptoms.

Running is incredibly powerful medicine.

But it isn't a force field.

Heart Symptoms Runners Shouldn't Ignore

Endurance athletes become accustomed to discomfort.

That's part of the sport.

Unfortunately, that mentality can make it easy to dismiss symptoms that deserve attention.

Talk with a healthcare professional if you experience symptoms such as unexplained chest pressure or pain, unusual shortness of breath, fainting or near fainting during exercise, unexplained decreases in performance, persistent heart palpitations, or unusually rapid or irregular heart rhythms.

This becomes particularly important for masters athletes because coronary artery disease becomes a more important cause of cardiac events as athletes age.

Being fit should never be a reason to ignore symptoms.

Should Older Runners Get a Coronary Calcium Scan?

This is where individualized medical advice becomes important.

A coronary artery calcium scan is a relatively quick CT scan that measures calcified plaque in the coronary arteries.

It can be useful for cardiovascular risk assessment in appropriately selected individuals, but that doesn't mean every runner should automatically get one.

Athletes also present an interesting challenge because we don't yet know whether a given CAC score carries exactly the same meaning in a lifelong endurance athlete as it does in a sedentary person.

The new joint European and American sports cardiology consensus highlights precisely this problem. Masters athletes can have cardiovascular findings that are difficult to interpret using guidelines developed primarily from sedentary populations.

If you're a masters endurance athlete with cardiovascular risk factors or a strong family history, discussing your individual risk with a physician familiar with sports cardiology may be worthwhile.

The Biggest Mistake Would Be to Stop Exercising

Research on extreme endurance exercise makes great headlines.

"Marathon Running Damages Your Heart."

"Too Much Exercise Causes Heart Disease."

"Ultrarunning Could Be Bad for You."

The reality is considerably less dramatic.

We have overwhelming evidence that physical activity reduces cardiovascular disease and mortality.

We also have emerging evidence that decades of extremely high endurance training may produce certain cardiovascular changes in some people.

Both things can be true.

The latest research doesn't tell us to stop exercising.

It tells us that the human response to exercise is more complicated than:

More exercise = infinitely more benefit.

At some point, the cardiovascular benefits may plateau while certain risks slowly increase.

Exactly where that point occurs and which athletes are susceptible remains uncertain.

The Bottom Line: Is Running Bad for Your Heart?

For most people:

Absolutely not.

Running is one of the most powerful things you can do to improve cardiovascular fitness and is consistently associated with lower cardiovascular and overall mortality.

Even small amounts appear beneficial.

But when we move from recreational running into decades of high volume marathon and ultramarathon training, the picture becomes more complicated.

Some lifelong endurance athletes appear to have higher rates of atrial fibrillation, coronary artery calcification, coronary plaque, and myocardial fibrosis.

We don't yet know exactly what all of these findings mean for longevity.

And importantly, endurance athletes still tend to have excellent cardiovascular fitness and favorable overall health outcomes.

So I'm certainly not hanging up my running shoes.

But I also don't think runners should assume that logging thousands of miles somehow makes us immune to heart disease.

Run. Train hard if that's what you enjoy. Take recovery seriously. Know your blood pressure and cholesterol. Pay attention to your family history. And don't ignore symptoms simply because you're fit.

Running is probably one of the best things you can do for your heart.

Just remember that more isn't automatically better forever.

References

1. Lee DC, Pate RR, Lavie CJ, Sui X, Church TS, Blair SN. Leisure Time Running Reduces All Cause and Cardiovascular Mortality Risk. Journal of the American College of Cardiology. 2014.
2. Pedisic Z, et al. Is Running Associated With a Lower Risk of All Cause, Cardiovascular and Cancer Mortality, and Is the More the Better? A Systematic Review and Meta Analysis. British Journal of Sports Medicine. 2020.
3. Franklin BA, et al. Exercise Related Acute Cardiovascular Events and Potential Deleterious Adaptations Following Long Term Exercise Training: Placing the Risks Into Perspective. Circulation. 2020.
4. Eijsvogels TMH, et al. Masters Athletes With Abnormal Cardiovascular Findings: A Clinical Consensus Statement of the European Association of Preventive Cardiology of the ESC and the American College of Cardiology. Journal of the American College of Cardiology. 2026.
5. Extreme Endurance Training and Coronary Artery Disease: A Systematic Review and Meta Analysis. International Journal of Cardiology. 2025.
6. Hsu JJ, et al. Paradox of Exercise and Coronary Artery Calcification: Potential Underlying Mechanisms. Circulation Research. 2025.
7. Fernandez AB, Chaudhry W, Thompson PD. Coronary Atherosclerosis in Masters Athletes: Mechanisms and Implications for Cardiovascular Disease Risk. Current Cardiology Reports. 2019.
8. Coronary Artery Disease in Masters Athletes: A Systematic Review. 2026.
9. Does Too Much Exercise Damage the Heart? A Narrative Review of the Long Term Cardiovascular Effects of Intense Training. European Journal of Preventive Cardiology. 2026.