Myocarditis symptoms:
how to recognize them and when to worry

Article written and reviewed by Dr Luca Moretti

Myocarditis can present in many different ways. The most common signs are chest pain or discomfort, shortness of breath, unusual fatigue, palpitations and a reduced ability to perform physical activities that were previously well tolerated. In some cases dizziness or fainting may occur; in more severe forms, signs of heart failure or a rapid deterioration in overall condition may develop.
No symptom, taken on its own, can diagnose myocarditis. If severe or persistent chest pain, marked breathing difficulty, loss of consciousness, or palpitations associated with feeling very unwell occur, urgent assessment is required and it may be appropriate to call 112 or 118.

Symptoms that may occur include:

• chest pain, pressure or discomfort;
• shortness of breath during exertion or, in more severe cases, even at rest;
• marked fatigue or a sudden reduction in exercise tolerance;
• palpitations or a fast or irregular heartbeat;
• dizziness, a feeling of being about to faint, or syncope;
• swelling of the legs and ankles or rapid weight gain due to fluid retention in forms associated with heart failure.

Myocarditis is inflammation of the heart muscle. This guide does not describe all the causes and histological forms of the disease: its purpose is to explain which symptoms may raise suspicion of myocarditis and which warning signs should not be ignored.

The most common symptoms of myocarditis

One of the difficulties with myocarditis is that there is no single clinical picture. Some people mainly have chest pain, others experience palpitations or heart rhythm disturbances, while others develop symptoms caused by reduced pumping function of the heart. There are also forms with few symptoms or that are discovered during investigations performed for other reasons.
Chest pain is a common presentation, especially in acute forms. It may feel like pressure or resemble pain from a coronary problem; when the inflammation also involves the pericardium it may have different features, for example changing with body position or breathing. However, the cause cannot be established with certainty from the type of pain alone.

Fatigue can vary greatly. In some cases it is simply a feeling of weakness or slower recovery after normal activities; in others it becomes evident because walking quickly, climbing stairs or carrying out usual activities causes breathlessness and fatigue that were not present before.
Fever, muscle aches, malaise or other symptoms of an infection may precede the heart problem, but they are not required for the diagnosis and are not specific to myocarditis.

Shortness of breath and reduced exercise capacity

Shortness of breath may occur when inflammation impairs heart function or when pressure rises inside the heart chambers. At first it may be noticeable only during activities that require exertion; in more severe forms it may occur with light activity or even at rest.
A rapid worsening of breathing, especially when associated with chest pain, severe weakness, pale skin or sweating, requires urgent assessment. Breathlessness should not automatically be attributed to a recent respiratory infection or simply to loss of fitness.

When heart failure develops, difficulty breathing while lying down, waking at night because of shortness of breath, swelling of the ankles and legs, or weight gain over a few days due to fluid accumulation may also occur. These signs do not necessarily indicate myocarditis, but they warrant medical assessment because they may signal a significant heart problem.

Palpitations, irregular heartbeat and fainting

Inflammation of the myocardium can interfere with the electrical system of the heart. For this reason, some people experience palpitations, a sensation of a very fast heartbeat, irregular beats or pauses. Not all palpitations are dangerous and many have benign causes, but they become more important when myocarditis is a possibility.
Particular attention is needed when palpitations are prolonged or are associated with chest pain, shortness of breath, severe weakness, dizziness or loss of consciousness. In these situations, an arrhythmia requiring prompt assessment may be present.

Syncope, meaning a transient loss of consciousness, is not a symptom that should simply be observed at home when heart disease is suspected. It can have many causes, but in myocarditis it may be related to a rhythm disturbance or to a reduction in the heart's ability to maintain adequate circulation.
Forms associated with electrical instability, rapidly progressive heart failure or shock are within the spectrum of the most severe presentations, including fulminant myocarditis, and require immediate hospital care.

Symptoms after an infection: when they deserve attention

Myocarditis can occur during or after an infection, but a temporal association is not enough to make the diagnosis. After flu, a respiratory infection or a gastrointestinal infection, it is normal to feel tired for a few days; what should increase concern is the onset of new cardiac symptoms such as chest pain, disproportionate shortness of breath, significant palpitations or syncope.
The timing of onset also varies. Cardiac symptoms may appear while the infection is still ongoing or later. Therefore, there is no time interval that, by itself, can confirm or exclude myocarditis.

When the clinical picture is mild and nonspecific, the doctor will assess the overall context and decide whether an ECG, blood tests or other investigations are indicated. When symptoms are significant, new or rapidly worsening, however, it is not appropriate to wait for them to resolve on their own.

When to call 112 or 118

Urgent medical care should be sought in the presence of severe or persistent chest pain, severe shortness of breath, loss of consciousness, confusion, marked weakness with a feeling of imminent fainting, or palpitations associated with a major deterioration in overall condition.
These symptoms are not specific to myocarditis: they may also be caused by a heart attack, pulmonary embolism, arrhythmias or other emergencies. For this reason, it is not advisable to try to determine the cause on your own at home.

If symptoms are less severe but persist, especially after a recent infection or in a person already diagnosed with myocarditis, it is still advisable to contact a doctor to determine the timing and type of assessment. Diagnosis requires integration of symptoms, physical examination, ECG, laboratory tests and, when indicated, cardiac imaging.

Frequently asked questions about myocarditis symptoms

What are the most common symptoms of myocarditis?
The most common symptoms include chest pain or discomfort, shortness of breath, fatigue, palpitations and reduced exercise tolerance. However, the presentation is highly variable, and some people may have mild or nonspecific symptoms.

Can myocarditis cause chest pain?
Yes. Chest pain is one of the most common presentations and may resemble the pain of a heart attack or, when the pericardium is also involved, have inflammatory features.

Can palpitations be a symptom of myocarditis?
Yes. Myocarditis can be associated with arrhythmias and cause palpitations or a fast or irregular heartbeat. Significant palpitations associated with fainting, chest pain or severe shortness of breath require urgent assessment.

Can myocarditis occur after an infection?
Yes. A recent infection may precede the onset of myocarditis, but simply having had a fever, flu or another infection does not prove that subsequent symptoms are caused by inflammation of the myocardium.

When do symptoms require urgent medical care?
Severe or persistent chest pain, marked breathing difficulty, loss of consciousness, palpitations associated with feeling very unwell or a rapid deterioration in overall condition require urgent assessment and may make it necessary to call 112 or 118.