Acute myocarditis: symptoms, diagnosis and recovery

The myocardium is the muscular wall of the heart. In myocarditis it becomes inflamed, which can reduce how effectively the heart pumps and can disturb the electrical signals that keep its rhythm regular. The British Heart Foundation explains that inflammation is the body's natural way of dealing with things that can harm it, such as infections or injuries, but in the heart it can cause symptoms that interfere with daily life.

The word acute describes an illness that develops over days or weeks rather than slowly over years. Myocarditis can occur once, recur or become long-lasting (chronic). It sometimes occurs together with pericarditis, inflammation of the sac around the heart, in which case it is called myopericarditis. The NHS describes pericarditis as causing sharp or stabbing chest pain that eases when leaning forward, which is why the two conditions can feel similar.

The BHF lists the common symptoms below, and notes that it is not unusual for them to begin up to two weeks after an infection. Some people have none; in them, myocarditis may be found during a routine appointment.

• Chest pain, discomfort or a feeling of tightness.

• Shortness of breath at rest, on exertion or when lying down.

• Unusual tiredness.

• Palpitations: the heart fluttering, racing or pounding, or an irregular heartbeat.

• Feeling light-headed or fainting.

• Flu-like symptoms such as a high temperature, headache, body aches, joint pain or sore throat.

• Rarely, swelling of the hands, legs, ankles or feet.

Viral infection is the most common trigger. The BHF describes how the immune system can overreact to a virus, and that this inflammation can stay in the heart even after the virus has gone, which explains the delay between the infection and the heart symptoms. Other causes it lists include bacterial infections, fungal infections, autoimmune diseases such as lupus, toxins such as carbon monoxide or drugs such as cocaine, and reactions to certain medicines or vaccines. It says there have been rare cases of myocarditis following some Covid-19 vaccines. Sometimes no cause is found.

Myocarditis can affect anyone of any age, including people who were fit and well beforehand, although the BHF says it tends to affect more males than females and people under 50. Myocarditis UK, a charity, highlights that symptoms can resemble other ailments, particularly in young people, which makes it hard to diagnose.

There is no single test. A doctor will examine you and ask about recent illnesses, autoimmune problems, exposure to toxins or drugs, and other risk factors, such as having recently had a baby. The BHF lists the usual tests as an electrocardiogram (ECG), an echocardiogram, a chest X-ray and blood tests, which are quick and mostly painless.

Cardiac MRI and a coronary angiogram may be used to help rule out other common heart causes, such as a blocked artery. In very rare cases a heart biopsy, taking a small sample of heart muscle for analysis, may be considered. Researchers funded by the BHF are working on a blood test specific to myocarditis, which is not yet available.

Treatment depends on the symptoms and the cause. According to the BHF it can include painkillers for the chest pain, medicines to calm the inflammation, antibiotics if a bacterial infection is the cause, and rest with plenty of fluids. A doctor will explain which anti-inflammatory medicines are suitable.

Most people have a single episode and recover with rest, medicine and avoiding high-intensity exercise while the heart recovers. Doctors follow progress closely at first, and a yearly follow-up appointment may then be offered. For some people myocarditis lasts longer or returns. If the inflammation scars the heart muscle, the heart can become enlarged and weaker, which is sometimes described as dilated cardiomyopathy or heart failure; in that case check-ups are at least every few months.

• Use pillows or sit forward with arms resting on a table if that eases breathing or chest discomfort.

• Wear loose clothing, stay hydrated and eat a diet rich in fruit and vegetables.

• Ask the heart team about a fit note if work is holding back recovery.

Returning to exercise is the question most people ask. The BHF says that generally it is recommended to avoid vigorous exercise for 3 to 6 months after a myocarditis diagnosis, and that you should ask your doctor how long to rest and what types of exercise are safe, because the condition affects people differently.

Time off work depends on symptoms and the job. A fit note (Statement of Fitness to Work) can be provided by a GP, and in England and Wales by some other health professionals. Questions worth raising at follow-up include the follow-up plan, tips for managing symptoms, and when exercise and work can restart.