Myocarditis and Sport

Myocarditis is inflammation of the heart muscle, usually triggered by a viral infection or the immune response to one, and an athlete with acute myocarditis must rest, not train through it.

It is a recognised cause of sudden cardiac death in young athletes. The danger is concentrated in the acute phase, when exercise can extend the injury and provoke a fatal arrhythmia. Myocarditis, pericarditis and the overlap between them are now grouped by the 2025 European Society of Cardiology (ESC) guidelines as inflammatory myopericardial syndromes, so chest pain after a virus needs assessment for heart muscle involvement rather than a label of simple pericarditis.

For the sport and exercise medicine (SEM) clinician this is often a first-contact problem: chest pain, breathlessness, palpitations or simply not recovering after a virus. The role is to recognise it, advise rest, refer, and guide a safe return rather than a premature one.

Most myocarditis follows viral infection, including enteroviruses such as Coxsackie, parvovirus B19, human herpesvirus 6, adenovirus and SARS-CoV-2, the virus that causes COVID-19. Much of the damage comes from the immune reaction rather than the virus itself. Non-viral causes include other infections, autoimmune and systemic inflammatory disease, certain drugs and toxins, and, rarely, vaccines: myocarditis after messenger RNA (mRNA) COVID-19 vaccination is usually mild and self-limiting and is seen mostly in young men.

The common thread is inflammation of the myocardium, the heart muscle.

Inflammation injures muscle cells, which can reduce pumping function, and disturbs the electrical properties of the muscle, creating a substrate for ventricular arrhythmias. During the active phase, the rise in cardiac demand with exercise can extend the injury and trigger these arrhythmias.

Many people recover completely. Some are left with persistent impairment or develop dilated cardiomyopathy, and a small number have a fulminant course with acute heart failure.