Myocarditis

• Myocarditis is inflammation of the heart muscle. In Western countries most cases are caused by viruses, but non-infectious immune and toxic causes exist.
• It mainly affects people under 40, yet it can present at any age and in many different ways: chest pain that looks like a heart attack, heart failure, palpitations or syncope.
• Many cases have a recent febrile or viral illness, but some do not. A normal ECG and a normal troponin do not exclude the diagnosis when suspicion is high.
• Cardiac magnetic resonance (CMR) using the updated Lake Louise criteria is the most powerful non-invasive test; it can provide a diagnosis without a biopsy in most patients.
• Treatment is usually supportive, with heart-failure and anti-arrhythmic therapy as needed; directed immunosuppression is reserved for specific forms such as giant cell, eosinophilic, cardiac sarcoid or immune checkpoint inhibitor myocarditis.
• Most patients recover, but myocarditis is one of the main causes of dilated cardiomyopathy, so treatment of the acute phase includes protecting the heart from persistent inflammation and reducing long-term scar.

By the end of this page you should be able to:

1. Define myocarditis and list its main infectious and non-infectious causes.
2. Explain how viral infection and the immune response damage heart muscle and why dilated cardiomyopathy can follow.
3. Recognise the three classic presentations and red flags that should raise suspicion.
4. Use the 2013 ESC diagnostic criteria to decide when a patient has clinically suspected myocarditis.
5. Describe what CMR shows in myocarditis and state the updated Lake Louise criteria.
6. Outline the initial treatment, criteria for intensive care, and when to refer to an advanced heart failure centre.
7. State the indications, cautions and regimens for immunosuppression by aetiology.
8. Give follow-up and return-to-exercise instructions and their evidence base.

The condition is classified by time course and histology. One practical classification recognises four forms: acute, fulminant, chronic active, and chronic persistent myocarditis.^[5] The 2025 European Society of Cardiology (ESC) guidelines use an umbrella term for the whole spectrum, inflammatory myopericardial syndrome (IMPS), because myocarditis and pericarditis often overlap in symptoms, cause and treatment.^[1]

A further distinction that matters clinically is between infectious myocarditis (most often viral) and immune-mediated or toxic myocarditis, where no organism is present but inflammation is driven by the immune system or by a drug or toxin. In many cases no definite cause is ever found, and the case is classed as idiopathic.^[5]

The 2024 American College of Cardiology (ACC) Expert Consensus Decision Pathway introduces a four-stage scheme that runs parallel to heart-failure staging and is useful for triage and follow-up.^[4]

• Stage A: at risk, with risk factors for myocarditis but no symptoms and no evidence of disease.
• Stage B: evidence of myocarditis (for example, abnormalities on CMR) without symptoms.
• Stage C: symptomatic myocarditis.
• Stage D: symptomatic myocarditis with haemodynamic or electrical instability.

Selected patients in Stage B, for example those whose myocarditis is related to an immune check-point inhibitor, and almost all patients in Stages C and D require active management, whereas Stage A calls for monitoring and counselling.

The exact incidence of myocarditis is difficult to estimate because many cases are silent and because diagnosis depends on whether a patient reaches specialist care. A 2019 Global Burden of Disease analysis estimated about 16 cases per 100,000 people per year worldwide.^[2] Incidence is higher in men (about 19 per 100,000 men per year) than in women (about 13 per 100,000 women per year), and it peaks in the third and fourth decades of life, with the highest risk between roughly 20 and 40 years.^[2] Nevertheless the condition can occur at any age, and the single most useful broad fact for bedside practice is that it primarily affects people under 40 years of age.^[5]

According to StatPearls, acute myocarditis accounts for about 65% of all myocarditis cases and is mainly viral, although non-infectious causes contribute.^[5]

Viral infections are the commonest identified cause in developed countries; in developing countries rheumatic carditis, Chagas disease and complications of advanced HIV infection are important.^[5] Viruses particularly associated with myocarditis are enteroviruses (coxsackie B), parvovirus B19, human herpesvirus 6, adenovirus, cytomegalovirus, Epstein-Barr virus and hepatitis C virus.^[2] These agents reach the myocardium either directly or through a post-viral immune response, and for practical care both routes are usually indistinguishable early on. SARS-CoV-2 infection can also cause myocarditis; during March 2020 to January 2021 COVID-19-associated myocarditis was reported to account for up to 41% of cases in some series, though the causal link has often been uncertain.^[2] Non-viral infectious causes include bacterial infection, rickettsial infection, Borrelia (Lyme disease), Trypanosoma cruzi (Chagas disease) and HIV.

• Immune-mediated diseases: systemic lupus erythematosus, eosinophilic granulomatosis with polyangiitis, giant cell arteritis and other connective tissue disorders, and sarcoidosis. Cardiac involvement in sarcoidosis is reported in 3 to 43% of patients with systemic disease.^[2]
• Drug- or toxin-induced myocarditis: hypersensitivity or direct toxicity from drugs such as clozapine, certain antibiotics, doxorubicin and other anthracyclines, methyldopa and interleukin-2, as well as cocaine, heavy metals and some venom or poisonous-animal exposures.
• Immune check-point inhibitor (ICI) myocarditis: an increasingly recognised complication of cancer immunotherapy. One report gives an incidence of about 1.14% among treated patients, and this form is often rapid and severe.^[2]
• Vaccine-associated myocarditis: a low but measurable risk, especially in young men after mRNA vaccines against COVID-19; most cases are mild and self-limiting. Reported peak incidence was about 105.9 cases per million in males aged 15 to 17 years.^[2]
• Rheumatic carditis, peripartum cardiomyopathy and a familial genetic predisposition.

The relative frequency of histological types in endomyocardial biopsy (EMB)-confirmed disease is heavily weighted to the common form: lymphocytic myocarditis about 95.5%, eosinophilic myocarditis about 3.6%, giant cell myocarditis about 0.007%, and ICI-associated myocarditis about 1.14%.^[2] Giant cell myocarditis is rare but aggressive, while eosinophilic myocarditis carries an in-hospital mortality of roughly 17%.^[2]

Male sex, age in the third or fourth decade, a recent febrile or viral illness, autoimmune disease, a family history of cardiomyopathy or sudden death, cardiotoxin exposure (cocaine, amphetamine), prior myocarditis, and ICI treatment all raise the likelihood.^[2][4] Genetic susceptibility is increasingly recognised, and some patients with apparently isolated myocarditis later turn out to have an inherited cardiomyopathy.^[4]

The common pathway in most cases is an initial injury phase followed by an immune phase.

1. Viral entry. Cardiotropic viruses attach to myocardial cell-surface receptors, enter myocytes and replicate. Direct viral damage can be modest, but it initiates the process.
2. Innate immunity. Viral RNA and cellular debris are detected by pattern-recognition receptors, leading to type I interferon responses and production of cytokines such as interleukin-1, interleukin-6 and tumour necrosis factor.
3. Adaptive immunity. Cytotoxic T cells infiltrate and kill infected and uninfected myocytes. In some patients cross-reactivity between the virus and myocardial proteins produces autoimmune injury that can continue after the virus has been cleared.
4. Remodelling. Loss of myocytes, oedema and extracellular-matrix changes weaken the wall, and the scar that follows stiffens the ventricle. Over weeks to years this produces dilation and systolic dysfunction, linking myocarditis to dilated cardiomyopathy.

In immune-mediated forms the trigger differs (a bacterial antigen, a drug, a self-antigen or a tumour antigen) but the downstream steps are similar. In giant cell myocarditis the infiltrate contains multinucleated giant cells and the course is fulminant; in eosinophilic myocarditis eosinophils dominate, often with a peripheral eosinophilia and systemic allergy or parasitic disease behind it; in cardiac sarcoidosis non-caseating granulomas and chronic fibrosis develop.

Damaged muscle also sets up electrical instability: arrhythmias, conduction block and, rarely, sudden death.

Biopsy, when performed, shows a diffuse or patchy inflammatory infiltrate with myocyte degeneration or necrosis. On cardiac magnetic resonance this corresponds to myocardial oedema, hyperaemia and capillary leak in the acute phase, and to a late gadolinium enhancement scar with a non-ischaemic (usually mid-wall or sub-epicardial) pattern once the inflammation subsides. In the healthy or healed stage the oedema has resolved and only scar remains. Baseline and follow-up imaging should look for this evolution.^[3]

Acute myocarditis has no pathognomonic symptoms, and the presentation spans a wide spectrum.^[3] The three classic presentations that the ACC ECDP emphasises are chest pain, heart failure and arrhythmia.^[4]

• Chest pain, pericarditic or pseudo-ischaemic. Often after a viral illness; the pain may be pleuritic or central, and the ECG may show diffuse ST elevation. It closely mimics acute coronary syndrome, especially in young patients without risk factors.
• Heart failure. Dyspnoea, orthopnoea, paroxysmal nocturnal dyspnoea, fatigue and exercise intolerance; with shock in the fulminant form.
• Arrhythmia or syncope. Palpitations, presyncope, syncope, aborted sudden death; ventricular tachycardia or high-grade atrioventricular block.

Prodromal symptoms suggestive of a preceding infection (fever, myalgia, respiratory or gastrointestinal upset) may be reported but their absence does not exclude the diagnosis.^[2] Many mild cases are never recognised and are found incidentally at autopsy or only after inflammation has produced end-stage heart disease.^[3]

Specific aetiologies declare themselves in characteristic ways. Lyme carditis and sarcoidosis can present with advanced conduction block in a patient whose left-ventricular function is near normal. Fulminant myocarditis declares itself as cardiogenic shock soon after a viral illness. Recurrent or family clustering raises the possibility of an inherited cardiomyopathy or auto-inflammatory syndrome.^[1][2]

Findings are often non-specific. Tachycardia, a pericardial friction rub when pericarditis coexists, gallop rhythms, a soft mitral regurgitation murmur from ventricular dilation, ventricular ectopy, or signs of left, right or biventricular failure may be present. Some patients have no signs at all and a normal examination.

A practical rule: in a young person with suspected acute coronary syndrome and no cardiovascular risk factors, ask about a recent febrile illness and consider myocarditis. The same applies to any unexplained dyspnoea or arrhythmia after a viral infection.^[3][4]

The first problem is clinical: is the patient's breathlessness, chest pain or arrhythmia due to myocarditis or to one of its common mimics? The second problem arises once a mass or mass-like picture is seen on imaging. Because myocarditis can look like many things, it remains a diagnosis of exclusion until investigations are complete.

No single test confirms or excludes myocarditis with certainty; an integrative approach is used.^[3]

A 12-lead ECG is usually abnormal, but the changes are neither sensitive nor specific.^[3] Findings include sinus tachycardia, non-specific ST-T changes, diffuse ST elevation that resembles pericarditis, PR depression, Q waves, reduced R-wave height, low voltage, axis change, frequent premature beats, supraventricular tachycardia, ventricular tachycardia or fibrillation, and atrioventricular block (first to third degree) or bundle branch block. A normal ECG does not exclude myocarditis, especially in a patient with strongly suggestive features.

High-sensitivity cardiac troponin is the most useful blood marker: it is elevated in myocarditis and, if normal, makes an acute myocardial injury unlikely. Creatine kinase-MB may also be raised. Inflammatory markers (C-reactive protein, erythrocyte sedimentation rate) and a white-cell count are often elevated but are non-specific, and eosinophilia suggests eosinophilic myocarditis.^[2] Raised biomarkers support the clinical suspicion and may be elevated in at least 60% of patients.^[2] Natriuretic peptides (BNP/NT-proBNP) help gauge heart-failure severity. Virology swabs and serum autoantibodies may suggest an aetiology in selected patients; routine viral serology is not recommended in most centres. Glucose, renal function and arterial blood gas are added for triage.

Transthoracic echocardiography is a first-line test in suspected myocarditis. It can rule out other diagnoses, estimate left- and right-ventricular size and function, detect pericardial effusion, intracavitary thrombus, and wall-motion abnormalities, and identify severe dysfunction that warrants intensive care. Classic findings include increased wall thickness early (oedema), mild segmental hypokinesia, ventricular dilation and systolic or diastolic dysfunction; regional wall-motion abnormalities do not follow a coronary territory. Prognosis is strongly linked to left-ventricular function.^[2] Speckle-tracking strain may improve detection of subtle acute myocarditis, although the evidence is still developing.

When a patient presents with chest pain suggestive of acute coronary syndrome, a non-invasive CT coronary angiogram or invasive angiography is frequently required to exclude coronary artery disease. Young patients with a classic history, no cardiovascular risk factors and immediate access to CMR may be able to avoid angiography.^[3]

CMR has become the cornerstone of non-invasive diagnosis in myocarditis and is now on par with endomyocardial biopsy in clinical utility for many patients.^[1] It characterises the myocardium directly: oedema (T2-based), hyperaemia and capillary leak (T1-based), necrosis and fibrosis (late gadolinium enhancement, LGE), pericardial involvement, global and regional function, and extracellular volume. Oedema appears as regional or global T1 and T2 prolongation; fibrosis appears as LGE in a non-ischaemic mid-wall or sub-epicardial distribution.^[3]

CMR performs best between 2 and 3 weeks from symptom onset, with the best-quality studies done early in the disease; LGE can be absent in the first 4 days, so studies performed very early need cautious interpretation.^[2] The strongest candidates for CMR are stable patients presenting with recent chest pain; it is less often diagnostic when heart failure or arrhythmia dominates. CMR is also the preferred tool for baseline characterisation before treatment decisions and for monitoring recovery.^[1]

The 2025 ESC guidelines recommend CMR in patients with clinically suspected myocarditis using the updated Lake Louise criteria for a non-invasive diagnosis, and recommend follow-up CMR within the first 6 months for risk stratification, individualised therapy and the decision about returning to exercise.^[1]

The diagnosis of acute myocardial inflammation on CMR is supported when one T2-based criterion for oedema and one T1-based criterion for myocardial injury are both positive.^[3]

Fulfilling both main categories increases specificity; a single positive category still supports the diagnosis in an appropriate clinical context, but with less specificity.^[3] Parametric mapping improves detection of diffuse or low-grade disease, which classic T2 or LGE imaging may miss, but it requires local reference ranges because values depend on scanner and sequence.^[3]

PET/CT can visualise myocardial inflammation and is valuable in the complex work-up of suspected cardiac sarcoidosis and in other complicated cases with inconclusive CMR or biopsy, and sometimes in recurrent myocarditis.^[3]

Non-invasive CT coronary angiography or invasive angiography is frequently performed when the presentation resembles acute coronary syndrome, mainly to exclude coronary stenosis of 50% or more.^[3] Ruling out significant CAD is part of the diagnostic logic of clinically suspected myocarditis.

EMB remains the reference standard for histological confirmation. It allows classification by infiltrating cell type (lymphocytic, eosinophilic, giant cell, granulomatous) and viral polymerase chain reaction (PCR) analysis, which helps to decide whether immunosuppression is safe.^[2] However, it is invasive, rarely used routinely, and has limited sensitivity because inflammation is patchy. Repeated sampling improves yield. Performance varies markedly with the clinical context: sensitivity is highest in giant cell myocarditis (about 80 to 93% with repeated biventricular sampling) and much lower in lymphocytic myocarditis and cardiac sarcoidosis (about 20 to 30%).^[2][3] All-cause complications are under 1% in experienced hands.^[3] EMB is currently recommended for fulminant, haemodynamically unstable, arrhythmic or heart-failure presentations; suspected giant cell, eosinophilic or sarcoid myocarditis; and cases in which histology would change therapy.^[1][2]

The 2013 ESC Working Group criteria, still widely referenced, define clinically suspected myocarditis as the presence of at least one clinical feature plus at least one diagnostic criterion from a different category, in the absence of angiographically detectable coronary artery disease (coronary stenosis of 50% or more) or of another known cardiovascular or extra-cardiac cause of the symptoms. If the patient is asymptomatic, at least two diagnostic criteria must be met. Suspicion increases the more criteria are fulfilled.^[3]

Routine viral serology is not recommended;^[3] virology and autoantibodies are used only in selected cases, for example to identify the aetiology of a specific syndrome.

Severity triage follows the overall clinical picture: left-ventricular function, haemodynamic stability, arrhythmia and conduction status. Poor outcomes are more likely with biventricular dysfunction, Stage D presentation, LGE on CMR and specific aetiologies such as giant cell myocarditis.^[4]

Management is built on four pillars: supportive care (heart failure and arrhythmia therapy), aetiology-directed therapy, haemodynamic support for unstable patients, and follow-up.

Haemodynamically stable patients with left-ventricular systolic dysfunction are managed according to current heart-failure guidelines, with early initiation of guideline-directed medical therapy: ACE inhibitors or ARBs/ARNI, beta-blockers, mineralocorticoid receptor antagonists, SGLT2 inhibitors and diuretics as needed. In patients with myocarditis and normal left-ventricular systolic function, the initiation of medical therapy is not recommended.^[2] Management of hemodynamically unstable patients requires intensive care, respiratory and mechanical cardiopulmonary support facilities; referral to a specialised tertiary centre is recommended. More severe presentations require plasma natriuretic peptide monitoring, vasopressors and inotropes, and if needed mechanical circulatory support. If a patient has not been weaned from mechanical support after 2 to 3 weeks, long-term left-ventricular assist device or transplantation should be considered.^[2]

Non-steroidal anti-inflammatory drugs and colchicine are used for pericardial-type chest pain, particularly when the pericardial component is prominent and ventricular function is preserved, similar to the regimen for acute pericarditis. They should be avoided in the presence of significant left-ventricular dysfunction, where they may worsen myocardial function. Colchicine has also shown promise by targeting the NLRP3 inflammasome, but large trial evidence is still limited.^[2]

Management of conduction disturbances, atrioventricular block and ventricular arrhythmias is usually supportive because these often resolve after the acute phase, but pacemakers or anti-arrhythmic drugs may be required. Implantable cardioverter-defibrillator (ICD) implantation is typically not recommended during the acute phase because arrhythmic risk often subsides within 3 to 6 months; a wearable cardioverter-defibrillator can serve as a bridge, although the evidence is limited.^[2] In a subset of patients with high arrhythmic risk, ICD implantation may be fast-tracked.^[2] A 2025 ESC recommendation table endorses ICD implantation for non-active myocarditis with haemodynamically tolerated sustained ventricular tachycardia (IIa, C) and for persistent risk factors for ventricular arrhythmias after the acute phase (IIb, C).^[1]

Immunosuppression is reserved for specific non-infectious forms, not given routinely to all patients, because trial evidence is limited and there is a risk of worsening active infection. Before starting therapy, viral genome should ideally be negative on the endomyocardial specimen; in high-risk or fulminant situations treatment may be started while results are awaited.^[2]

Giant cell myocarditis in particular requires prompt initiation of immunosuppression, with transplant considered in selected cases; transplant-free clinical remission has been reported in up to 65% of treated patients, and antithymocyte globulin plus high-dose methylprednisolone and cyclosporine is used in fulminant disease. ^[2]

• Left-ventricular systolic dysfunction and heart failure, sometimes weeks after onset.
• Conduction defects and tachyarrhythmias, including ventricular tachycardia and fibrillation.
• Cardiogenic shock in fulminant myocarditis; mechanical circulatory support may be needed.
• Left-ventricular thrombus with systemic or pulmonary embolism.
• Pericarditis and effusion (myopericarditis).
• Progression to chronic inflammatory cardiomyopathy and dilated cardiomyopathy.
• Recurrence after apparent recovery.
• Sudden cardiac death from ventricular arrhythmia or heart block.

Prognosis is very heterogeneous and follows the presentation and the aetiology. One ACC summary of biopsy-proven disease reports roughly 50% resolution within 2 to 4 weeks, 25% developing persistent cardiac dysfunction, and 12 to 25% progressing to end-stage heart failure or death.^[4] Predictors of poor outcome include biventricular dysfunction, Stage D presentation, LGE on CMR and specific aetiologies such as giant cell myocarditis.^[4] Acute complications are more likely when acute decompensated heart failure, sustained arrhythmias, reduced left-ventricular function or need for inotropes, vasopressors or mechanical support are present.^[5] Conversely, patients who survive the acute phase generally do well and CMR features of healing (resolution of oedema) are reassuring; persistent late gadolinium enhancement, however, carries an adverse prognostic signal.^[3]

Long-term studies describe a substantial minority developing cardiomyopathy, and giant cell myocarditis remains dangerous without treatment, although immunosuppression has converted it from an almost uniformly fatal disease into one with a high probability of transplant-free remission.

Myocarditis is both a model and a recognised cause of dilated cardiomyopathy: inflammation damages and kills myocytes, and the repair process replaces functioning muscle with fibrous scar, so the ventricle dilates and pumps less efficiently. This inflammatory dilated cardiomyopathy may present months after the acute illness, sometimes with no clear history of cardiac symptoms, and accounts for a large share of newly diagnosed, unexplained non-ischaemic cardiomyopathy in young adults.^[2][3] Because of this, the acute-phase goal is not just to relieve symptoms but to limit permanent myocardial loss: prompt supportive therapy, removal of the trigger where possible, monitored follow-up imaging to detect non-recovery, and a low threshold for referring patients with residual dysfunction, arrhythmia or scar burden to an advanced heart-failure service. Patients should be counselled that a normal initial echocardiogram does not guarantee full recovery, and that repeat imaging at 6 months is part of standard care.

There is no specific vaccine against the common viral causes of myocarditis. Prevention is general: common-sense infection control, avoiding cardiotoxins (heavy alcohol, cocaine, amphetamine), and appropriate screening of family members where an inherited cardiomyopathy is suspected. In patients with a personal history of myocarditis, information about symptoms and a return plan is offered before discharge. Athletes and other physically active people should follow structured return-to-play assessment rather than arbitrary calendar rest.

• Children. Myocarditis in children is frequently viral and can be fulminant; management follows the same principles but uses paediatric heart-failure and immunosuppression protocols and early transfer to a paediatric cardiology centre. Specific evidence in children is an area of active research.
• Pregnancy. Peripartum cardiomyopathy and viral myocarditis can overlap. Care is best coordinated by a cardio-obstetric and heart-failure team; diagnostic and therapeutic decisions must balance maternal and fetal safety.
• Older adults. Coronary artery disease is a more likely cause of cardiac dysfunction; exclusion of ischaemia is correspondingly more important.
• Immunocompromised patients. Opportunistic or reactivated infections, including Chagas-related and HIV-related myocarditis, are more likely and need targeted, pathogen-specific treatment.

• A standard transthoracic echocardiogram plus troponin and ECG will classify severity and guide referral where CMR is unavailable.
• Coronary disease may need exclusion with CT or angiography only when risk factors exist; in low-risk young patients, observation and referral may suffice.
• Colchicine and common anti-inflammatory drugs are inexpensive and helpful when a pericardial component dominates.
• Escalate early to a regional centre that can provide intensive care and, ideally, mechanical support before irreversible shock develops.

Light-touch plain-text references only; no verified topic links are used in this first version.

• Dilated cardiomyopathy
• Pericarditis and myopericarditis
• Acute coronary syndrome
• Heart failure, acute and chronic
• Cardiac magnetic resonance imaging
• Cardiac sarcoidosis
• Sudden cardiac death and implantable cardioverter-defibrillators