--- title: Athlete's heart description: What athlete's heart is, which changes in the heart and the ECG are normal in trained people, how doctors tell them apart from heart disease, why the heart is checked before competitive sport, and when to call an ambulance. type: disease aliases: - athletic heart - exercise-induced cardiac remodeling - exercise-induced cardiac remodelling - EICR sources: - tier: guideline org: esc title: 2020 ESC Guidelines on sports cardiology and exercise in patients with cardiovascular disease year: 2020 doi: 10.1093/eurheartj/ehaa605 url: https://doi.org/10.1093/eurheartj/ehaa605 - tier: guideline org: minzdrav-rf title: Желудочковые нарушения ритма сердца. Внезапная сердечная смерть year: 2025 doi: 10.15829/1560-4071-2025-6670 url: https://cr.minzdrav.gov.ru/view-cr/569_2 - tier: guideline org: minzdrav-rf title: Гипертрофическая кардиомиопатия year: 2025 doi: 10.15829/1560-4071-2025-6387 url: https://cr.minzdrav.gov.ru/view-cr/283_2 - tier: guideline org: minzdrav-rf title: Брадиаритмии и нарушения проводимости year: 2025 doi: 10.15829/1560-4071-2025-6669 url: https://cr.minzdrav.gov.ru/view-cr/160_2 - tier: review title: 'Clinical Considerations for Competitive Sports Participation for Athletes With Cardiovascular Abnormalities: A Scientific Statement From the American Heart Association and American College of Cardiology' year: 2025 doi: 10.1161/CIR.0000000000001297 url: https://doi.org/10.1161/CIR.0000000000001297 - tier: reference org: msd-manuals title: Athlete's Heart (Exercise-Induced Cardiac Remodeling) (MSD Manual Professional Version) year: 2026 url: https://www.msdmanuals.com/professional/cardiovascular-disorders/sports-and-the-heart/athlete-s-heart - tier: reference org: msd-manuals title: Athlete's Heart (MSD Manual Consumer Version) year: 2026 url: https://www.msdmanuals.com/home/heart-and-blood-vessel-disorders/sports-and-the-heart/athlete-s-heart - tier: reference org: msd-manuals title: Sudden Cardiac Death in Athletes (MSD Manual Professional Version) year: 2026 url: https://www.msdmanuals.com/professional/cardiovascular-disorders/sports-and-the-heart/sudden-cardiac-death-in-athletes sources_checked: 2026-10-14 review: null --- Athlete's heart is a set of changes in the structure and function of the heart in people who train for long periods and/or at high intensity. It is the heart's normal response to regular strenuous exercise: both endurance exercise, such as higher-intensity running or cycling, and heavy weight training. The heart walls become thicker and the chambers somewhat larger, but the heart and its valves work normally. Athlete's heart matters because some of its signs look like the signs of dangerous diseases, such as [hypertrophic cardiomyopathy](../hypertrophic-cardiomyopathy/), and the doctor has to tell them apart. The rare sudden death of an athlete is usually caused by a heart disease that had not been found before, not by the changes of athlete's heart.

The diagram shows the heart in section: the two atria on top, the two ventricles below. This is the heart of a person who does not train long and hard: the chambers and walls are of usual size, and the resting pulse is usual. The changes of athlete's heart appear in people who train a lot.

In a trained athlete, the mass of the left ventricle, the thickness of its wall and the size of its cavity increase over time, and the resting pulse becomes slower. Uniform enlargement is typical of athlete's heart: all four chambers become a little larger, and the wall thickens symmetrically. The heart still works normally: this is an adaptation to training, not a disease. The dashed line shows the outline of a heart of usual size, for comparison.

## Why it happens When a person trains regularly and for long periods, the heart has to pump more blood and work against higher pressure. Over time the muscle of the left ventricle becomes heavier, its wall thicker and its cavity larger. Such a heart pumps more blood with each beat, so it can beat more slowly: an athlete's pulse is usually slower and stronger than that of an untrained person of the same age. What the changes look like depends on the amount of training and the type of sport. In women the changes are usually smaller than in men of the same age, body size and level of training. According to MSD, this applies to people who train for prolonged durations (for example, more than 1 hour most days) and/or frequently at high intensity. Volume and pressure loads increase LV muscle mass, wall thickness and chamber size; maximal stroke volume and cardiac output increase, the resting heart rate falls mainly because of increased vagal tone, and systolic and diastolic function remain normal. According to ESC 2020, LV cavity enlargement without systolic dysfunction and outside the context of a familial disease is a physiological adaptation if it is consistent with the type of sport (usually endurance sports) and the body size; a mildly reduced EF with an enlarged LV should not merely be considered an adaptation, and assessment of LV function during exercise is then useful. ## Symptoms Athlete's heart itself causes no symptoms. It is usually noticed by chance: at a routine check-up or during tests for another reason. The doctor may notice a slow pulse and a heart murmur; some murmurs are perfectly normal in an athlete and are not dangerous. At rest the heartbeat may be irregular, but it becomes regular when exercise begins. If an athlete has chest pain, breathlessness or palpitations, athlete's heart does not explain them: a heart disease has to be looked for. Fainting in athletes is most often harmless, for example reflex fainting or fainting after exercise, but fainting during exercise needs a full heart check. Possible examination findings: bradycardia, a systolic ejection (flow) murmur at the left lower sternal border, and a third heart sound due to early, rapid diastolic filling; a fourth heart sound is almost always abnormal in an athlete. [Atrial fibrillation](../atrial-fibrillation/) is more prevalent in active and former male master athletes and in those performing high-intensity endurance sports; this association has not been confirmed in women. ## How it is diagnosed Athlete's heart is a diagnosis of exclusion: the doctor makes it only after making sure there is no dangerous disease with similar signs, such as a cardiomyopathy or coronary heart disease. Most athletes do not need extensive testing, but an ECG is often done. Some ECG changes that would be abnormal in an untrained person are normal in an athlete. If there are symptoms or the ECG raises questions, the next tests are a heart ultrasound (echocardiography), an exercise test and sometimes a heart MRI. The doctor takes into account the type of sport, the intensity of training, age, sex, height and weight, and draws the final conclusion from all the findings together. Sometimes, if the tests have not given an answer, the doctor suggests reducing or stopping training for a few months to see whether the changes go away. Only the doctor decides this. Before taking part in competitions, athletes have a heart check to find diseases that carry a risk of sudden death before the first symptoms appear. For young athletes this means questions about health, an examination and an ECG; for older athletes, an assessment of heart disease risk. **ECG.** The most common finding is sinus bradycardia. Sinus bradycardia, first-degree AV block and Mobitz I block are normal in competitive athletes; marked conduction abnormalities require further evaluation. According to the Russian Ministry of Health bradyarrhythmia guideline (160_2), bradycardia in highly trained athletes can be considered normal only if it is asymptomatic and the heart rate rises adequately with exercise. In the MSD table (international standards for ECG interpretation in athletes), findings that need no further evaluation if there are no symptoms and no family history of sudden cardiac death or inherited heart disease include isolated voltage criteria for hypertrophy, incomplete right bundle branch block, early repolarisation, sinus bradycardia of 30 bpm or more, and first-degree or second-degree type 1 AV block with a PR interval of 200–399 ms. Findings that need further evaluation include T-wave inversion (other than the normal variants), ST depression, pathological Q waves, pre-excitation, a prolonged QT interval, bradycardia below 30 bpm, a PR interval of 400 ms or more, and second-degree type 2 or third-degree AV block (see the article on [AV block](../av-block/)). Many resting ECG changes decrease with exercise, which distinguishes athlete's heart from disease, but a normal exercise test does not exclude a cardiomyopathy. **The "grey zone" and HCM.** HCM is diagnosed when there is unexplained LV wall thickness of ≥ 15 mm in any segment. There is no single threshold for the zone of overlap: according to ESC 2020 it is 12–15 mm in some male athletes, while female athletes rarely have a wall thicker than 12 mm; according to the Russian Ministry of Health HCM guideline (283_2), differential diagnosis is needed at 13–15 mm; according to MSD, the zone of overlap is 13–15 mm in men and 11–13 mm in women. Features in favour of athlete's heart are balanced enlargement of all four chambers, symmetric hypertrophy, no family history of cardiomyopathy or sudden death, and, with LV dilation, symmetric enlargement of the RV and atria. If echocardiography does not exclude disease, cardiac MRI helps; late gadolinium enhancement usually favours HCM, but its absence does not exclude the disease. **Detraining.** The changes of athlete's heart should regress after training stops while a cardiomyopathy should persist, but sometimes the features of a cardiomyopathy also seem to resolve, so the result is interpreted with caution; MSD advises using this approach only when a thorough evaluation, including MRI and genetic testing, has not given an answer. **Screening.** Pre-participation screening is supported by all major societies, but the best method for young athletes (under 35) remains controversial. The Russian Ministry of Health guideline on ventricular arrhythmias (569_2) recommends history, physical examination and a 12-lead ECG for young athletes, cardiovascular risk assessment before high-intensity exercise for those over 35, and, when abnormalities are found, echocardiography and/or cardiac MRI. ECG screening outperforms history and physical examination, but there is insufficient evidence to recommend routine echocardiography. ## How it is treated Athlete's heart is not treated: it is the heart's normal response to heavy training. When a person stops training, the heart size and pulse usually return gradually to normal; this can take weeks or months. Sometimes the changes remain for a long time, and it is not known whether they are harmful. If the tests find a heart disease with a risk of sudden death, the question is about that disease, not about athlete's heart: the doctor assesses whether training can continue under the current sports eligibility rules. Decisions about training and taking part in competitions are made by the doctor together with the athlete. No treatment is required. Usually the structural changes and bradycardia regress with detraining, but about 20 % of elite athletes have residual chamber enlargement, and without long-term data it is unclear whether this is truly benign. For asymptomatic competitive athletes with abnormal ECG findings, AHA/ACC suggest considering a temporary break from competitive sport during the evaluation. For an established disease with a risk of sudden death, the Russian Ministry of Health guideline requires an assessment of eligibility under the current rules. ## When to call an ambulance **An athlete suddenly collapses and does not regain consciousness** — this may be cardiac arrest. What to do and what happens in cardiac arrest is described in detail in the article on [ventricular fibrillation](../ventricular-fibrillation/). - Call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK) straight away and start cardiopulmonary resuscitation. - Bring and use an automated external defibrillator as quickly as possible: the Russian Ministry of Health guideline stresses that it should be used as early as possible, within minutes, and that defibrillators should be placed in accessible spots in sports halls and arenas. With prompt resuscitation and early use of a defibrillator, many athletes survive. Fainting during exercise needs a full heart check, especially if the person collapsed suddenly, without warning, or had sudden palpitations, chest pain or severe breathlessness beforehand; until the check is finished, the athlete is kept out of competitions. For fainting, chest pain or severe breathlessness during exercise, call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK): this is the site's general safety rule, repeated at the bottom of every page. It is not urgent, but do see a doctor if a pre-participation ECG showed abnormalities or if there have been cases of sudden death or inherited heart disease in your family.