Exercise. Diet. Smoking cessation. These are the top three most accessible lifestyle choices we have to influence heart health. It’s well known that exercise alone carries incredible benefits for strengthening the cardiovascular system. And when combined with a healthy diet and not smoking, the payoff is bigger, reducing our risk of chronic diseases, including arrhythmias like atrial fibrillation (AFib).
For cardiac patients, though, exercise can feel like a double-edged sword. Different types and intensities of activity interact with the heart in various ways, which can make knowing what’s “safe” feel confusing.
So, how does exercise affect the heart in general?
How does it interact specifically with AFib?
And when does “too much exercise” become counterproductive?
The Cardiovascular Benefits of Exercise
The heart is a highly adaptable muscle. In the same way biceps get stronger after repeated weight training, the heart remodels itself in response to exercise, which, in general, is healthy and productive.
When you exercise, your muscles demand more oxygen. To keep up, your heart has to pump faster and more forcefully. Increased demand is supported through structural and electrical changes, including left-ventricular dilation, increased heart rate, improved contractility, and enhanced blood flow to working muscles. These adaptations are collectively known as “cardiac remodeling.“1
Over time, exercise can:
- Strengthen the heart muscle
- Reduce resting heart rate
- Improve blood vessel flexibility and function
- Lower blood pressure
- Enhance metabolic health
These changes are overwhelmingly positive when exercise is performed at low to moderate intensity, and they’re the main reasons physical activity lowers cardiovascular disease risk and increases lifespan.
Exercise has a “dose-dependent” benefit, meaning more activity corresponds with better cardiovascular outcomes up to a point. International cardiology guidelines recommend a minimum of 150 minutes per week of moderate exercise or 75 minutes of vigorous exercise.2
Exercise and Afib
Atrial fibrillation (AFib) is the most common sustained arrhythmia in clinical practice, and it carries elevated risks of stroke, heart failure, and cardiovascular events. Believe it or not, exercise is still recommended to Afib patients for healthy heart functioning – but the type, intensity, and duration of your workout matter more than the average bear.
When studying several popular cardio workouts, researchers found that:3
- Moderate-intensity continuous training (MICT) consistently reduces AFib incidence and improves symptoms.
- High-intensity interval training (HIIT) yields benefits equal to or greater than MICT in some patients, including improved exercise capacity and reduced AFib burden.
- Excessive high-endurance exercise, however, can increase AFib risk due to atrial remodeling, inflammation, and increased vagal tone. (Vagal tone is the level of “braking power” the vagus nerve has on heart rate – helpful in moderation, but too much can make the heart more prone to rhythm disturbances. And while atrial remodeling is usually a good adaptation in healthy training, extreme endurance leads to maladaptive remodeling – stretching and scarring of the atria that makes AFib more likely.)
Moderate-intensity continuous training (MICT)
MICT corresponds to activities like brisk walking, steady cycling, light jogging, or low-impact aerobics – typically 3 to 5.9 metabolic equivalents (METs), meaning they require about three to six times the energy you’d use at rest.
A 12-year follow-up of over 80,000 adults found that more than one hour of MICT daily reduced AFib risk in men, and that women experienced progressively reduced risk as activity levels increased.3
High-intensity interval training (HIIT)
HIIT alternates short bursts of high-intensity activity (≥6 METs, meaning more than six times your resting energy output) with recovery intervals. If you were on a stationary bike, for instance, this would look like one minute of fast cycling followed by one to two minutes of easy pedaling, repeated several times.
One randomized controlled trial even found that two weekly 23-minute HIIT sessions were as effective as two 60-minute MICT sessions in patients with persistent or permanent AFib.3
Researchers were able to demonstrate that exercise exerts anti-arrhythmic benefits through several mechanisms:
- Reduced overall inflammation in the body
- Increased anti-inflammatory mediators (a “cool-down crew” that helps settle irritation in heart tissue)
- Improved antioxidant capacity
- Enhanced fibrinolytic activity (the ability to break down small clots)
- Improved endothelial nitric oxide production (increase in “relax and flow” molecules that protect the heart)
- Better autonomic balance (healthier equilibrium between the body’s “speed up” and “slow down” systems)
In other words, exercise strengthens the heart and reduces the environmental “triggers” that promote atrial fibrillation.
Too Much of a Good Thing
Most people can safely exercise without experiencing negative cardiac effects. However, research shows that long-term high-intensity endurance training (such as marathon running, elite cycling, or intense daily workouts) can cause electrical remodeling that may produce:,4
- Bradycardia
- Atrioventricular (AV) block
- T-wave inversions on ECG
- Increased ectopic beats
While this sounds alarming, these changes generally occur in elite athletes, not the average person. For most, exercise remains protective, not risky.
It’s also understood among clinicians that a sedentary lifestyle is significantly more dangerous than the potential risks of high exercise levels.5 For cardio patients, Afib and otherwise, it’s important to work with a healthcare professional to strike a healthy balance between exercising enough and exercising too much – not exercising at all just isn’t going to cut it.
One of the most compelling studies on exercise and AFib used data from accelerometers (like Fitbits) rather than self-reported exercise habits (which can be less objective and, therefore, less reliable).5 After following the data on over 6,000 people for five years, they found:
- Each hour of exercise per week lowered AFib risk by 11%.
- Up to 150 minutes per week reduced AFib risk by 38%.
- 151 to 300 minutes per week reduced risk by 60%.
- 300+ minutes per week reduced risk by 65%.
On the flipside, prolonged high-intensity exercise, like that of elite athletes, can actually increase AFib risk, as well as the risk of other cardiovascular issues.
Researchers point out that everyday exercisers have little to worry about, but it’s still a good idea to know what overtraining or aggravation of an arrhythmia look like:
- Unusual palpitations
- Chest discomfort
- Persistent fatigue
- Unexplained shortness of breath
- Decreased exercise capacity
- Dizziness or faintness
Safe guidelines, including for those with Afib, emphasize moderate intensity and avoiding sudden spikes in exercise duration or intensity. It’s also important to listen to your body and tune into what feels normal for you.
Even for most cardiac patients, exercise is cardio-protective. Rather than avoiding exercise, find the right intensity, stay consistent, and partner with your healthcare team to create a plan that supports long-term heart rhythm stability, reduces arrhythmia aggravation, and promotes overall cardiovascular health.
Dr. Tordini is a part of Florida Medical Clinic Orlando Health
- George, S. A., Trampel, K. A., Brunner, K., & Efimov, I. R. (2024). Moderate Endurance Exercise Increases Arrhythmia Susceptibility and Modulates Cardiac Structure and Function in a Sexually Dimorphic Manner. Journal of the American Heart Association, 13(9), e033317–e033317. https://doi.org/10.1161/jaha.123.033317.
- Mannakkara, N. N., & Finocchiaro, G. (2023). Exercise and the Heart: Benefits, Risks and Adverse Effects of Exercise Training. Reviews in cardiovascular medicine, 24(3), 94. https://doi.org/10.31083/j.rcm2403094.
- Wang, Y., Wang, Y., & Xu, D. (2024). Effects of different exercise methods and intensities on the incidence and prognosis of atrial fibrillation. Trends in Cardiovascular Medicine, 34(8), 510–515. https://doi.org/10.1016/j.tcm.2024.01.002.
- George, S. A., Trampel, K. A., Brunner, K., & Efimov, I. R. (2024). Moderate Endurance Exercise Increases Arrhythmia Susceptibility and Modulates Cardiac Structure and Function in a Sexually Dimorphic Manner. Journal of the American Heart Association, 13(9), e033317–e033317. https://doi.org/10.1161/jaha.123.033317.
- Arrhythmia Alliance. (2025). Just 1 Hour of Weekly Exercise May Lower AFib Risk, but More Is Still Better. Heartrhythmalliance.org. https://heartrhythmalliance.org/us/just-1-hour-of-weekly-exercise-may-lower-afib-risk-but-more-is-still-better.
