Myocarditis

What happens in myocarditis

Infection or an immune reaction causes inflammatory cells to enter the heart muscle. This can:

• damage heart muscle cells, releasing troponin into the blood
• weaken the heart's pumping (reduced ejection fraction)
• disturb the electrical system, causing irregular rhythms
• cause scarring that may persist

When the surrounding sac (pericardium) is also inflamed, it is called myopericarditis.

Causes

Infections

• Viruses (most common): coxsackievirus and other enteroviruses, adenovirus, parvovirus B19, human herpesvirus 6, influenza, COVID-19, HIV, hepatitis C
• Bacteria: Lyme disease, diphtheria, streptococcus
• Parasites: Chagas disease (in Latin America)

Non-infectious causes

• Autoimmune and inflammatory diseases: lupus, sarcoidosis, giant cell myocarditis, inflammatory bowel disease
• Medicines: immune checkpoint inhibitors used for cancer, clozapine, some antibiotics, and hypersensitivity reactions
• mRNA COVID-19 vaccines: rare, mostly in males aged 12 to 29, usually within a week after the second dose, typically mild and resolving quickly
• Toxins: cocaine, alcohol, radiation

Symptoms

• chest pain, sharp or pressure-like, sometimes worse lying down (if the pericardium is involved)
• shortness of breath, at rest or with activity
• palpitations or irregular heartbeat
• fatigue and reduced exercise tolerance
• lightheadedness or fainting
• leg swelling with heart failure
• fever, aches and other recent viral symptoms

Children may have breathlessness, fast breathing, poor feeding or fainting. Some people have no symptoms at all, and myocarditis is a known cause of sudden cardiac death in young athletes.

Myocarditis vs pericarditis vs heart attack

Diagnosis

• ECG: may show changes resembling a heart attack, or rhythm problems
• Troponin: a blood marker of heart muscle injury
• Inflammatory markers and viral tests
• Echocardiogram: checks pumping function and wall motion
• Cardiac MRI: the key noninvasive test, showing inflammation and scarring
• Coronary angiography or CT to rule out a heart attack
• Endomyocardial biopsy: a tiny sample of heart muscle, used in severe or unexplained cases, or suspected giant cell myocarditis

Treatment

Mild myocarditis

• rest and avoiding strenuous exercise and competitive sports for at least 3 to 6 months
• treatment of the underlying infection when possible
• monitoring with repeat tests

Heart failure and rhythm problems

• heart failure medicines such as ACE inhibitors or ARBs, beta-blockers and diuretics
• treatment of arrhythmias, sometimes with an implantable cardioverter-defibrillator (ICD) for dangerous rhythms
• in severe cases (fulminant myocarditis), intensive care with mechanical heart support or, rarely, a heart transplant

Immune treatments

Steroids and other immunosuppressants are used for specific types, such as giant cell, eosinophilic, sarcoid and checkpoint inhibitor-related myocarditis.

Things to avoid

• strenuous exercise during recovery
• alcohol and recreational drugs
• NSAIDs may be avoided in myocarditis with reduced heart function; follow your cardiologist's advice

Complications

• dilated cardiomyopathy and chronic heart failure
• dangerous heart rhythms and sudden cardiac death
• recurrence

Recovery and outlook

Most people with mild myocarditis and preserved heart function recover completely within weeks to months. Vaccine-related myocarditis is usually mild with rapid recovery. Severe cases may leave lasting heart damage. Before returning to competitive sport, guidelines advise repeat echocardiogram, Holter monitoring, exercise testing and sometimes MRI after 3 to 6 months.

Frequently asked questions

What are the symptoms of myocarditis?

Common symptoms include chest pain, shortness of breath, palpitations, fatigue, lightheadedness or fainting, and sometimes leg swelling. They often follow a viral illness by days to weeks. Some people have no symptoms.

What causes myocarditis?

Viral infections are the most common cause, including coxsackievirus, adenovirus, influenza and COVID-19. Other causes include autoimmune diseases, certain medicines, toxins and, rarely, mRNA COVID-19 vaccines.

How long does it take to recover from myocarditis?

Mild cases often recover within weeks, but the heart needs time to heal fully. Strenuous exercise should be avoided for at least 3 to 6 months, and return to sport depends on follow-up heart tests.

Can myocarditis go away on its own?

Many mild cases resolve with rest and supportive care, but medical evaluation and follow-up are needed because myocarditis can cause heart failure or dangerous rhythms. Exercise restrictions are important even if you feel well.

Is myocarditis from the COVID vaccine serious?

It is rare and usually mild, mostly affecting young males within a week of the second mRNA dose. Most people recover quickly with rest and pain relief. COVID-19 infection itself carries a higher risk of myocarditis than vaccination.