Yes. Myocarditis, which is inflammation of the heart muscle, has rarely been reported after some vaccines, especially mRNA COVID-19 vaccines. The risk is highest in adolescent and young adult males, often during the week after vaccination, but cases can occur in other people. Most reported cases improve with care, although some may have lasting heart changes. New chest pain, trouble breathing, or a racing heartbeat needs urgent medical assessment.
The possibility of myocarditis after vaccination is an established but uncommon safety concern, particularly with certain COVID-19 vaccines. Understanding which vaccines have been associated with this condition, when symptoms may appear, and how healthcare professionals evaluate possible cases can help put the risk into perspective. Myocarditis can also develop after infections and from other causes, so symptoms appearing after vaccination do not automatically establish the cause.
Which vaccines have been linked to myocarditis?
The clearest evidence of a link between vaccination and myocarditis concerns mRNA COVID-19 vaccines, including the Pfizer-BioNTech and Moderna vaccines. These vaccines have been associated with rare cases of inflammation affecting the heart muscle. The U.S. Centers for Disease Control and Prevention (CDC) also notes evidence suggesting an increased risk of myocarditis and pericarditis following Novavax COVID-19 vaccination.
Myocarditis is inflammation of the heart muscle, which helps the heart pump blood around the body. Pericarditis is inflammation of the thin sac surrounding the heart. The two conditions can occur together, but they are not identical. Both have been reported after certain COVID-19 vaccinations, and either condition may cause chest discomfort or breathing difficulties.
These findings should not be interpreted as meaning that myocarditis is a common reaction to vaccination or that all vaccines carry the same risk. The evidence is specific to particular vaccines and populations. Reports of a health problem after vaccination also need clinical assessment because timing alone cannot determine whether the vaccine caused it.
How common is myocarditis after COVID-19 vaccination?
Myocarditis following COVID-19 vaccination is rare, although its frequency differs across age groups, sexes, vaccine types, and doses. According to the U.S. Food and Drug Administration (FDA), an analysis of health insurance claims estimated approximately 8 cases of myocarditis and/or pericarditis per million doses of the 2023–2024 mRNA COVID-19 vaccines among people aged 6 months through 64 years. The estimate was approximately 27 cases per million doses among males aged 12 through 24 years. These figures cover the first seven days after vaccination and combine both conditions.
These estimates describe a specific vaccine formulation, time window, and population. They are not estimates for every vaccine or every age group, and they should not be used to predict an individual's likelihood of developing myocarditis. Vaccine safety monitoring continues, and estimates may change as researchers collect and analyze additional information.
Who has a higher risk of vaccine-associated myocarditis?
The risk has been observed most often in adolescent and young adult males following mRNA COVID-19 vaccination. Cases have occurred more frequently after the second dose in the original multidose vaccination schedules, although myocarditis has also been reported in females, other age groups, and after other doses.
The CDC's COVID-19 vaccine safety guidance emphasizes that cases have most frequently occurred in adolescent and young adult males within seven days after a second mRNA vaccine dose. This pattern helps healthcare professionals recognize when further evaluation may be appropriate, but it does not mean that people outside this group cannot develop myocarditis.
Age and sex are population-level patterns, not diagnostic criteria. A healthcare professional considers the person's recent vaccination history alongside symptoms, previous illnesses, examination findings, and possible alternative explanations.
When can myocarditis symptoms begin after vaccination?
When myocarditis is associated with an mRNA COVID-19 vaccine, symptoms commonly begin within several days of vaccination and most often within the first week. This timing is a useful clinical clue, particularly when someone develops new chest pain or breathing problems after a recent dose. However, symptoms can also have other causes, and the timing alone cannot confirm vaccine-associated myocarditis.
Ordinary short-term reactions to vaccination, such as a sore arm, tiredness, headache, or muscle aches, are more common and generally improve within a few days. Symptoms that suggest possible heart involvement require a different level of attention, especially when they are new, persistent, or worsening.
What symptoms can occur?
Myocarditis can cause different symptoms depending on how the heart muscle is affected. Some people experience relatively mild symptoms, while others develop more serious problems with heart function or heart rhythm. Symptoms reported with myocarditis after vaccination can include:
- New or persistent chest pain or discomfort.
- Shortness of breath, including difficulty breathing during ordinary activities.
- Palpitations, such as a racing, pounding, or irregular heartbeat.
- Unusual tiredness or reduced ability to carry out normal activities.
- Lightheadedness or fainting.
These symptoms are examples of possible experiences, not a checklist for identifying myocarditis. Similar symptoms may occur with other heart or lung conditions, infections, and non-cardiac problems. Their presence after vaccination deserves appropriate assessment rather than an assumption about the cause.
What should you do if symptoms appear after vaccination?
Seek immediate medical assessment if you develop new or persistent chest pain, shortness of breath, or a racing or pounding heartbeat after vaccination. If you have severe chest pain, major difficulty breathing, fainting, or rapidly worsening symptoms, contact local emergency services or seek emergency care immediately. Do not wait for symptoms to disappear or assume they are an ordinary vaccine reaction.
Tell the healthcare professional which vaccine you received, the date of vaccination, when your symptoms started, and whether you recently had an infection or another illness. This information can help guide the evaluation. If symptoms are concerning, assessment should not be delayed simply because they began several days after the injection rather than immediately afterward.
How do doctors diagnose myocarditis after vaccination?
There is no single symptom or test that establishes every case of myocarditis. Healthcare professionals consider the vaccination timeline, medical history, physical examination, and test results together. According to Mayo Clinic's guidance on myocarditis diagnosis, evaluation may include blood tests, an electrocardiogram (ECG), an echocardiogram, and cardiac magnetic resonance imaging (MRI).
Blood tests may help identify inflammation or signs of heart muscle injury. An ECG records the heart's electrical activity and can reveal certain rhythm or electrical changes. An echocardiogram uses sound waves to show how the heart is structured and how well it pumps blood. Cardiac MRI can provide detailed images that help clinicians assess inflammation and injury in the heart muscle.
Not every person needs every test. The healthcare team chooses investigations according to the symptoms, examination, initial results, and other possible causes. The evaluation may also consider a recent viral infection, including COVID-19, because infections are recognized causes of myocarditis.
Does myocarditis after vaccination usually improve?
Many people diagnosed with myocarditis after mRNA COVID-19 vaccination improve with medical care, and symptoms often resolve. Treatment depends on the person's condition and may involve rest, medication, monitoring, or hospital care when necessary. The course is not identical for everyone, and an uncomplicated early recovery does not by itself establish that all heart inflammation has resolved.
Longer-term outcomes remain an important area of follow-up. In its June 2025 safety communication, the FDA discussed follow-up research in people who developed myocarditis after mRNA COVID-19 vaccination. Some participants continued to show abnormal findings on cardiac MRI several months later, but the long-term clinical significance of these imaging findings remains uncertain.
For this reason, people diagnosed with myocarditis should attend recommended follow-up appointments. A clinician may reassess symptoms, heart function, or imaging findings and determine when normal activities can safely resume. Recovery should be based on the individual's medical evaluation rather than on a fixed timetable.
Can you exercise after vaccine-associated myocarditis?
People who have been diagnosed with myocarditis should avoid strenuous exercise and competitive sports until their healthcare team confirms that it is safe to return. Physical activity places additional demands on the heart, and the appropriate period of restriction depends on the individual's condition and recovery.
The timing of a return to exercise should be guided by follow-up evaluation, which may include symptoms, heart rhythm, heart function, and other relevant test results. Do not use the disappearance of chest pain or fatigue alone as proof that strenuous activity is safe.
Should a previous episode affect future vaccination?
A history of myocarditis after vaccination should be discussed with a qualified healthcare professional before another vaccine dose is given. The appropriate advice depends on the original diagnosis, its suspected cause, the vaccine involved, the person's recovery, and the current recommendations for that vaccine. Decisions may differ when myocarditis followed an infection or another cause rather than vaccination.
Do not assume that every person with a previous episode must permanently avoid all vaccines. Equally, do not assume that receiving another dose is automatically appropriate. A clinician can review the available evidence and weigh the potential benefits and risks for the person's circumstances.
For COVID-19 vaccination, recommendations can change as vaccine formulations and safety evidence evolve. People with a documented history of vaccine-associated myocarditis should obtain individualized advice based on current guidance rather than relying on older reports or advice intended for the general population.
How does vaccination risk compare with myocarditis from infection?
Vaccination is not the only possible setting for myocarditis. Viral infections, including COVID-19, can also cause inflammation of the heart muscle. Other recognized causes include certain medicines and inflammatory or autoimmune conditions, and in some cases the exact cause is never established.
Distinguishing these possibilities is important when symptoms appear after vaccination. A recent injection may be relevant to the assessment, but healthcare professionals must also consider whether the person has an infection or another condition that could explain the findings. The aim is to identify the most likely cause and assess any effect on heart function so that appropriate care can be provided.