# Acute Myocarditis

Acute myocarditis requires rapid separation of uncomplicated inflammatory myocardial injury from acute coronary syndromes, fulminant shock, malignant arrhythmia, and biopsy-defined inflammatory syndromes requiring cause-directed immunosuppression or mechanical circulatory support.

**Clinical question:** How should physicians diagnose, risk-stratify, and manage suspected acute myocarditis while identifying patients requiring biopsy or circulatory support?

Updated: 2026-08-24T17:11:48.346330+00:00

## What matters in practice
- Treat cardiogenic shock, sustained ventricular arrhythmia, or high-grade atrioventricular block as complicated myocarditis and escalate immediately to an advanced heart failure or critical care setting capable of mechanical circulatory support and endomyocardial biopsy. [2][3][21]
- In suspected acute myocarditis, obtain high-sensitivity troponin and use cardiac MRI as the principal noninvasive test for myocardial inflammation; the 2018 Lake Louise criteria improve diagnostic accuracy. [6][8][24]
- Chest pain with elevated troponin requires exclusion of acute coronary syndromes and other myocardial-injury mimics before assigning myocarditis as the working diagnosis. [1][9][19]
- Use guideline-directed heart failure and arrhythmia treatment when ventricular dysfunction or clinical heart failure is present; avoid initiating beta-blockers in heart block. [4][12][23]
- Restrict intense exercise after acute myocarditis and consider return to sport only after 3 to 6 months when the patient is asymptomatic, ventricular function is normal, inflammation has resolved, and arrhythmias are absent. [18][22]

## Identify complicated or fulminant myocarditis before completing the etiologic workup

Hemodynamics, rhythm, and conduction status determine disposition and urgency of invasive evaluation.

Admit patients with suspected myocarditis who have acute heart failure, hemodynamic instability, syncope with suspected arrhythmia, sustained ventricular arrhythmia, high-grade atrioventricular block, or rising troponin with evolving ventricular dysfunction. Fulminant myocarditis presents with sudden severe diffuse myocardial inflammation and may progress to cardiogenic shock, often requiring intravenous inotropes or mechanical circulatory support (MCS). [2][3][21]

For cardiogenic shock, manage in an intensive care environment and involve advanced heart failure, interventional cardiology, electrophysiology, and cardiac surgery early. MCS is a bridge to recovery, diagnosis, or transplantation in patients whose perfusion cannot be maintained with pharmacologic support; the need for MCS should also accelerate planning for endomyocardial biopsy (EMB). [2][11][13][21]

Place patients with new atrioventricular block, ventricular tachycardia, or ventricular fibrillation on continuous telemetry. Avoid beta-blockers in clinically significant heart block; use antiarrhythmics cautiously when ventricular dysfunction is present because negative inotropy may worsen heart failure. Patients with heart block may require pacing. [3][23]
- Treat acute pulmonary congestion and ventricular dysfunction with heart-failure-directed therapy, including diuretics when volume overloaded; use inotropic support when low output or shock is present. [23]
- Avoid NSAIDs in suspected viral myocarditis because they may impair myocardial healing and worsen inflammation. [23]
- Do not delay circulatory-support evaluation while awaiting cardiac MRI in shock or rapidly progressive ventricular failure. [2][21]

*Disposition by high-risk clinical presentation. [2][3][18][21]*

| Presentation | Immediate action | Diagnostic consequence |
| --- | --- | --- |
| Cardiogenic shock or rapidly progressive severe LV failure | ICU care; inotropic support and early MCS-capable advanced heart failure consultation. [2][3][21] | Urgently evaluate for EMB when results may identify a treatable inflammatory subtype. [11][21] |
| Sustained ventricular arrhythmia or resuscitated cardiac arrest | Continuous monitoring and acute arrhythmia management in a monitored setting. [3][22] | Treat as complicated myocarditis; evaluate structural disease and inflammatory substrate. [18][22] |
| New high-grade AV block | Telemetry; assess need for temporary pacing; avoid beta-blocker initiation. [3][23] | Escalate evaluation for an inflammatory myocarditis phenotype requiring targeted treatment. [22][23] |
| Stable chest pain or mild heart-failure presentation | Obtain ECG, high-sensitivity troponin, echocardiography, and evaluate for coronary disease and other mimics. [6][9][19] | Proceed to cardiac MRI when clinical suspicion remains. [6][8][24] |

## Confirm myocardial inflammation while excluding acute coronary syndrome and other mimics

No isolated clinical feature establishes myocarditis; combine presentation with objective noninvasive abnormalities.

Use the presenting syndrome to frame testing: acute chest pain, acute heart failure, new or recurrent unexplained arrhythmia, and cardiogenic shock are compatible clinical presentations. A suspected diagnosis is supported by at least one compatible presentation plus a diagnostic abnormality on noninvasive testing; asymptomatic patients require at least two diagnostic criteria. [18][19]

Obtain a 12-lead ECG, serial high-sensitivity troponin, and transthoracic echocardiography. Elevated troponin is a common trigger for suspicion, but chest pain with troponin elevation also requires evaluation for acute coronary syndrome before myocarditis is assigned as the explanation. Echocardiography defines ventricular function and detects clinically important heart-failure physiology, while strain imaging may add diagnostic information in selected suspected cases. [6][9][10][19]

Cardiac MRI is the noninvasive test of choice for suspected myocarditis because it evaluates myocardial edema and injury. Apply the 2018 Lake Louise criteria, which have high diagnostic accuracy and improve diagnostic performance relative to original criteria. MRI should complement, not replace, urgent invasive evaluation in unstable patients. [7][8][24]
- Trend troponin rather than using a single value to determine whether myocardial injury is ongoing; interpret the result with symptoms, ECG, ventricular function, and coronary evaluation. [6][9][19]
- Use echocardiography early to identify LV dysfunction, pericardial involvement, or hemodynamic consequences that alter admission level and treatment. [10][19]
- Use cardiac CT or invasive coronary evaluation when coronary anatomy must be clarified in a patient with chest pain and elevated troponin. [6][9]

### When to pursue endomyocardial biopsy

Consider EMB when myocarditis is complicated by shock, severe acute heart failure, high-grade atrioventricular block, or ventricular arrhythmias, particularly when histology could identify an inflammatory subtype requiring disease-specific immunosuppression. EMB is selectively required in fulminant presentations and remains the classic confirmatory diagnostic method for myocarditis. [11][21][22][23]

Use biopsy findings to distinguish lymphocytic inflammation from eosinophilic myocarditis, giant cell myocarditis, cardiac sarcoidosis, or other inflammatory myocardial diseases. This distinction matters because autoimmune, giant cell, eosinophilic, and sarcoid-associated myocarditis may require maintenance immunosuppressive therapy rather than heart-failure treatment alone. [20][21][22]
- Do not use a stable cardiac MRI result as a reason to defer EMB in a deteriorating patient when histology could alter urgent treatment. [2][11][21]
- Coordinate EMB with a center able to provide MCS or transplant-level support when fulminant physiology is present. [2][13][21]

*Diagnostic branch points in suspected acute myocarditis. [6][8][9][19][22][24]*

| Finding | Interpretation | Next step |
| --- | --- | --- |
| Chest pain plus elevated high-sensitivity troponin | Myocardial injury; acute coronary syndrome and myocarditis are both plausible. [6][9][19] | Assess ECG and coronary disease; obtain echocardiography and cardiac MRI if suspicion for myocarditis persists. [6][8][9] |
| Compatible syndrome plus noninvasive diagnostic abnormality | Supports clinically suspected myocarditis. [19] | Risk-stratify by ventricular function, rhythm, and hemodynamics; use MRI for noninvasive tissue characterization. [8][18][19] |
| Cardiac MRI meeting 2018 Lake Louise criteria | Supports acute myocardial inflammation with improved diagnostic accuracy over original criteria. [24] | Manage phenotype and severity; consider EMB if unstable or if pathology would change treatment. [21][22] |
| Shock, malignant arrhythmia, or high-grade AV block | Complicated myocarditis with potential biopsy-defined treatable disease. [2][3][22] | ICU-level management, early MCS assessment, and EMB consideration. [2][11][21] |

## Use exposure history and pathology to identify myocarditis requiring cause-directed treatment

Most patients need phenotype-guided supportive care; selected etiologies change the urgency and type of immunosuppression.

Ask specifically about recent viral illness, autoimmune disease, new cancer immunotherapy, vaccination, cardiotoxic medication exposure, travel or epidemiologic risk, and systemic allergic or eosinophilic features. Viral infection is the most frequent cause in the United States and other developed countries, but myocarditis also follows autoimmune disease, vaccination, and cancer therapy. [16][23]

Immune checkpoint inhibitor (ICI)-associated myocarditis is rare but potentially fatal. In a patient receiving cancer immunotherapy who develops troponin elevation, conduction disease, ventricular arrhythmia, heart failure, or compatible cardiac MRI findings, treat ICI exposure as a high-priority etiologic clue and coordinate urgent cardio-oncology evaluation; Lake Louise criteria can support MRI diagnosis in this setting. [1][7]

Biopsy-directed treatment is most consequential when EMB identifies eosinophilic myocarditis, giant cell myocarditis, cardiac sarcoidosis, or autoimmune myocarditis. Maintenance immunosuppression is often required for autoimmune disease-associated myocarditis and for sarcoid, giant cell, or eosinophilic myocarditis; empiric intravenous corticosteroids are described for fulminant myocarditis or myocarditis causing acute heart failure, high-grade AV block, or ventricular arrhythmias. [20][22]
- Do not assume a recent viral syndrome establishes viral myocarditis or excludes other causes; biopsy becomes more valuable when the course is fulminant or electrically unstable. [21][23]
- In ICI-exposed patients, lower the threshold for urgent monitoring and multidisciplinary evaluation because myocarditis may be rapidly fatal. [1]
- Reserve longer-term immunosuppressive strategies for a defined inflammatory phenotype or systemic autoimmune condition rather than uncomplicated presumed viral myocarditis. [20][22]

*Etiologic patterns that alter the next action. [1][7][16][20][22][23]*

| Clinical clue | Priority diagnosis | Actionable next step |
| --- | --- | --- |
| Recent flu-like illness, often 7 to 14 days before presentation | Viral myocarditis. [23] | Provide phenotype-based heart failure and rhythm treatment; avoid NSAIDs. [23] |
| Active or recent immune checkpoint inhibitor therapy | ICI-associated myocarditis. [1] | Urgent cardio-oncology assessment; cardiac MRI may support diagnosis, and assess for complicated disease requiring biopsy-directed care. [1][7][22] |
| Autoimmune disease or biopsy evidence of eosinophilic, giant cell, or sarcoid myocarditis | Immune-mediated inflammatory myocarditis. [20][22] | Use pathology and systemic disease assessment to guide corticosteroid-based and, when needed, maintenance immunosuppression. [20][22] |
| Shock, ventricular arrhythmia, or high-grade AV block regardless of trigger | Fulminant or complicated myocarditis. [2][3][22] | Prioritize ICU stabilization, MCS assessment, and EMB consideration over outpatient etiologic testing. [2][11][21] |

## Treat ventricular dysfunction and arrhythmias now, then reassess recovery before return to exercise

Therapy is determined by hemodynamic phenotype and biopsy-defined etiology rather than by inflammation alone.

For myocarditis with heart failure or ventricular dysfunction, initiate and titrate guideline-directed medical therapy as tolerated, using diuretics for congestion and standard heart-failure therapy for persistent systolic dysfunction. Acute myocarditis presenting as dilated cardiomyopathy is managed primarily with an optimal heart-failure regimen. [4][12][23]

Manage arrhythmias according to clinical stability and ventricular function, recognizing that antiarrhythmic drugs can worsen heart failure through negative inotropy. Maintain monitoring for ventricular arrhythmias and conduction deterioration during the acute phase; use pacing when clinically significant heart block requires it. [3][22][23]

Restrict physical activity until symptoms resolve and inflammatory markers normalize. At least 1 month may be needed for clinical remission, but return to sports should generally wait 3 to 6 months and requires absence of symptoms and arrhythmias, no ongoing inflammation, and normal LV systolic function. [18][22]
- Reassess LV systolic function and arrhythmia status before clearing strenuous exercise or competitive sport. [18]
- Continue heart-failure therapy when ventricular dysfunction persists rather than stopping treatment solely because acute symptoms improve. [4][12]
- Escalate refractory heart failure despite standard therapy to an advanced heart failure team because MCS or transplantation may be required. [13][22]

### Monitoring priorities after discharge

Follow recovery using symptoms, ventricular systolic function, inflammatory activity, and rhythm assessment, because return-to-play decisions require normal LV function, absence of arrhythmias, and no evidence of ongoing inflammation. Persistent ventricular dysfunction should continue to be managed as myocarditis-related cardiomyopathy with guideline-directed heart-failure therapy. [4][18]
- Do not clear athletic activity on symptom resolution alone; document the required functional, inflammatory, and rhythm recovery criteria. [18]
- Reevaluate patients with recurrent chest pain, worsening heart failure, syncope, new conduction disease, or ventricular arrhythmia for recurrent or persistent inflammatory myocardial disease. [18][19][22]

*Treatment and activity decisions by clinical phenotype. [4][12][18][22][23]*

| Phenotype | Management priority | Monitoring or restriction |
| --- | --- | --- |
| Congestive heart failure with ventricular dysfunction | Diuretics for congestion and guideline-directed heart-failure therapy as tolerated. [4][12][23] | Reassess LV function; continue therapy when dysfunction persists. [4][12] |
| Low-output state or cardiogenic shock | Inotropic support and early MCS assessment in an advanced center. [2][13][21][23] | Use intensive hemodynamic and rhythm monitoring; evaluate for EMB. [2][11][21] |
| High-grade AV block or ventricular arrhythmia | Continuous monitoring; pacing when needed; use antiarrhythmics cautiously in ventricular dysfunction. [3][22][23] | Document absence of arrhythmia before return to strenuous exercise. [18] |
| Clinical recovery after acute myocarditis | Maintain activity restriction until remission criteria are met. [18] | Consider sport resumption after 3 to 6 months only with normal LV function, no arrhythmias, no ongoing inflammation, and no symptoms. [18] |

## References
1. Myocarditis and look-alikes: when the diagnosis matters — heart.bmj.com — https://heart.bmj.com/content/early/2026/01/20/heartjnl-2025-326381.abstract
2. Recognition and Initial Management of Fulminant Myocarditis — www.ahajournals.org — https://www.ahajournals.org/doi/10.1161/CIR.0000000000000745
3. Diagnosis and Management of Myocarditis in Children — www.ahajournals.org — https://www.ahajournals.org/doi/10.1161/CIR.0000000000001001
4. Management of Myocarditis-Related Cardiomyopathy in ... — www.ahajournals.org — https://www.ahajournals.org/doi/10.1161/CIRCRESAHA.118.313578
5. Clinical Characteristics and Mechanisms of Acute Myocarditis — www.ahajournals.org — https://www.ahajournals.org/doi/10.1161/CIRCRESAHA.124.324674
6. Multimodality imaging in acute myocarditis — onlinelibrary.wiley.com — https://onlinelibrary.wiley.com/doi/10.1002/jcu.23310
7. Immune checkpoint inhibitor-related myocarditis: an illustrative ... — academic.oup.com — https://academic.oup.com/ehjcr/article/6/1/ytab478/6513876
8. Assessing the Accuracy of Cine Post‐Contrast Cardiac ... — onlinelibrary.wiley.com — https://onlinelibrary.wiley.com/doi/10.1002/ird3.70088
9. Advanced Computed Tomography and Magnetic ... — onlinelibrary.wiley.com — https://onlinelibrary.wiley.com/doi/10.1111/echo.70106
10. The Utility of Strain Echocardiography in the Diagnosis ... — onlinelibrary.wiley.com — https://onlinelibrary.wiley.com/doi/full/10.1111/echo.70443
11. a position statement of the European Society of Cardiology ... — academic.oup.com — https://academic.oup.com/eurheartj/article/34/33/2636/408735
12. The management of myocarditis - Oxford Academic — academic.oup.com — https://academic.oup.com/eurheartj/article/32/21/2616/439730
13. Update on myocarditis – what we know so far and where we may be ... — academic.oup.com — https://academic.oup.com/ehjacc/article-pdf/10/4/455/39217565/zuaa065.pdf
14. Myocarditis associated with COVID-19 and its vaccines — www.sciencedirect.com — https://www.sciencedirect.com/science/article/abs/pii/S0033062022001049
15. Review Paradigm shift in myocarditis treatment — www.sciencedirect.com — https://www.sciencedirect.com/science/article/pii/S0914508723002034
16. Modeling immune checkpoint inhibitor associated ... — www.sciencedirect.com — https://www.sciencedirect.com/science/article/pii/S277297612400062X
17. “Bridging the clinical, molecular and genetic perspectives on myocarditis in post-COVID-19 era” — www.sciencedirect.com — https://www.sciencedirect.com/science/article/pii/S2772487526000061
18. Evolution in the Diagnosis and Treatment of Myocarditis in Recent Years: State of the Art — pmc.ncbi.nlm.nih.gov — https://pmc.ncbi.nlm.nih.gov/articles/PMC12608363
19. Acute Myocarditis - StatPearls - NCBI Bookshelf — www.ncbi.nlm.nih.gov — https://www.ncbi.nlm.nih.gov/books/NBK441847
20. Advances in myocarditis management in the light of the latest research and recent guidelines of the European Society of Cardiology — pmc.ncbi.nlm.nih.gov — https://pmc.ncbi.nlm.nih.gov/articles/PMC11076022
21. Fulminant Myocarditis: When One Size Does Not Fit All – A Critical Review of the Literature - PMC — pmc.ncbi.nlm.nih.gov — https://pmc.ncbi.nlm.nih.gov/articles/PMC10316338
22. Myocarditis: Diagnostic Modalities and Treatment Options — pmc.ncbi.nlm.nih.gov — https://pmc.ncbi.nlm.nih.gov/articles/PMC11873950
23. Viral Myocarditis - StatPearls - NCBI Bookshelf — www.ncbi.nlm.nih.gov — https://www.ncbi.nlm.nih.gov/books/NBK459259
24. Comparison of Original and 2018 Lake Louise Criteria for ... — pubs.rsna.org — https://pubs.rsna.org/doi/abs/10.1148/ryct.2019190010

## Editorial note

Prepared from cited clinical literature using Astra's research workflow. Verify recommendations against current guidance and patient-specific factors.