Picture of heart as a muscle

Exercise and the heart

Can the effects of intense exercise on the heart be dangerous?

Skeletal muscles grow if they are worked hard, and so does the heart muscle. Increased cardiac efficiency goes with getting fit – but can an enlarged heart be dangerous?

Athletic heart syndrome

The left ventricle is the main pumping chamber of the heart, and athletes who train hard for hours every day tend to have more powerful left ventricles, with more muscle, thicker walls and a larger blood-pumping chamber. This goes along with a slower resting heart rate, as each beat moves more blood.

These changes are referred to as ‘athletic heart syndrome’ (AHS) and are normally harmless.

Hypertrophic cardiomyopathy

However, AHS looks similar on several standard heart tests to an inherited enlargement and stiffening of the heart wall called hypertrophic cardiomyopathy. This condition makes it harder to pump blood out of the heart and around the body, which can lead to light-headedness, fainting, an irregular heartbeat and even sudden cardiac arrest, where the heart suddenly stops beating without warning.

Hypertrophic cardiomyopathy is a genetic condition, with approximately 1 in 500 people affected by the disease in the UK. Some people may not have many symptoms, if any, but early diagnosis is vital to avoid the risk of sudden cardiac arrest.

A problem for athletes

Sadly, a small number of athletes have died during sports events because, while they appeared to be fit and healthy, they unknowingly had inherited cardiomyopathy, and suffered sudden cardiac arrest while exercising. The problem is that because the condition is characterised by an enlarged, thickened wall in the left ventricle – similar to AHS – among athletes it can easily go undiagnosed.  

So, while AHS isn’t a life-threatening condition, it can be dangerous, as it can disguise a very dangerous disease. Athletes with enlarged hearts may find their doctors want to examine them very closely because of the similarities between a trained and malformed heart.


About this resource

This resource was first published in ‘Exercise, Energy and Movement’ in January 2012 and reviewed and updated in August 2016.

Physiology, Health, infection and disease
Exercise, Energy and Movement
Education levels:
14–16, 16–19, Continuing professional development