Recent heart failure signs with systolic dysfunction, no other cause AHA 2021 Figure 3 names congenital heart disease, coronary abnormality and familial cardiomyopathy., plus (AHA 2021 Figure 3):
Viral prodrome within 1–4 weeks
ST-segment changes or T-wave inversion
Chest pain or pericarditic findings
Ventricular arrhythmias or heart block
Elevated troponin
LV dysfunction out of proportion to LV dilation
ESC 2025 red flags ESC 2025 Table 6, myocarditis: recent or concomitant flu-like syndrome or gastroenteritis; infarct-like chest pain; palpitations; heart failure symptoms; ECG changes; ventricular arrhythmias (isolated, complex); syncope; haemodynamic instability; raised hs-Tn or CK-MB; raised NT-proBNP; abnormal wall motion, increased wall thickness or impaired systolic function on imaging; myocardial oedema and/or LGE on CMR. Red flags raise awareness; they are not a risk grade. · Neonates JCS 2023: nonspecific (fever, hypothermia, dysphoria, poor suckling, vomiting, respiratory distress, seizures); also arrhythmia, cardiogenic shock, sudden death; prenatal infection may present as nonimmune fetal hydrops; meningitis, hepatitis or DIC may accompany it. Reported neonatal mortality 31–50%.
Presenting features in children, %
AHA 2021 Table, corrected version: reported frequencies in pediatric myocarditis
History
Symptoms
Signs
Viral prodrome 41–69
Fatigue 25–70
Tachypnea 52–60
Arrhythmias 11–45
Shortness of breath 35–69
Tachycardia 32–57
Syncope 4–10
Fever 31–58
Hepatomegaly 21–50
Sudden cardiac death (frequency not estimable)
Nausea, vomiting or abdominal pain 28–48
Respiratory distress 21–47
Rhinorrhea 38–44; cough 17–44
Murmur 26; gallop 20
Chest pain 24–42; dyspnea 22–25
Diminished pulses 16–21
Palpitations 16; diarrhea 8
Edema 7; cyanosis 2
Myocarditis was found in 6% of young athletes with sudden cardiac death in the US (AHA 2021, corrected from 9%).
About 80% of children with a definitive diagnosis were seen at least twice before diagnosis (JCS 2023; its Table 44 restates the AHA 2021 ranges with some differences).
ESC 2025: 1–2 cases per 100 000 children a year; very young children are predisposed to severe myocarditis.
How certain is the diagnosis
ESC 2025 Table 4 Clinical presentation: chest pain or infarct-like symptoms, arrhythmias, heart failure, aborted sudden cardiac death. Additional criteria: non-specific clinical findings; ST-T changes on ECG; troponin elevation; abnormal strain, wall motion or reduced EF; myocardial oedema and/or LGE on CMR. CMR proven = 2 of 2 updated Lake Louise main criteria; uncertain = 1 of 2; rejected = negative CMR. EMB proven, uncertain or rejected by pathologist consensus. ESC 2025 §12.2.1: its diagnostic approach applies also to children.
Category
Criteria
Definite
Clinical presentation and CMR- or EMB-proven
Possible
Clinical presentation + ≥1 additional criterion; CMR or EMB uncertain or not available
Unlikely/rejected
Clinical presentation only
AHA 2021 (children) strata: biopsy proven; CMR-confirmed clinically suspected; clinically suspected; possible. Figure 1. Clinically suspected: supportive findings when biopsy and CMR cannot be done, or despite negative results. No clinical criteria alone confirm myocarditis or separate suspected from possible. A positive biopsy proves it; a negative biopsy or CMR does not rule it out. Confirmation by biopsy or CMR is encouraged, weighing patient safety and CMR capability. Unlike ESC 2025, AHA 2021 keeps “proven” for biopsy.
Tests: graded recommendations
ChildrenJCS 2023 Table 45 AHA 2021 (children) gives no classes of recommendation; graded statements here are from JCS 2023 and ESC 2025, each with its own class labels.
Class
Recommendation
LOE
I
Cardiac enzymes and troponins; echocardiography; cardiac MRI
C
IIa
Transcatheter endomyocardial biopsy can be considered
ECG; echocardiography; histology of myocardium taken at ECMO start or VAD implantation
C
IIa
Cardiac enzymes and troponin can be considered
C
IIb
Transcatheter endomyocardial biopsy may be considered
C
AdultsChildrenESC 2025 Recommendation Tables 1, 5 ESC 2025 proposes its approach in adults; §12.2.1 says the diagnostic approach applies also to children, and §16 calls the uncertainties especially pronounced in children. These rows and the Table 7 risk grades (which feed its Figure 5 diagnostic algorithm) are diagnostic; the ESC rows on Shock Team, circulatory support, genetic testing and follow-up are not restated for children.
AdultESC 2025: genetic testing should be considered in definite myocarditis with a family history of IMPS or (suspected) inherited cardiomyopathy, severe ventricular arrhythmia, significant LGE (e.g. ring-like or septal) or persistent LV systolic dysfunction, or recurrent myocarditis or persistent troponin elevation (IIa, B). Family history with pedigree in recurrent IMPS (I, C).
Adult ESC 2025: CMR at follow-up, at least within the first 6 months (I, C); clinical review, biomarkers (at least troponin), ECG, exercise test, Holter, echocardiography and CMR within 6 months of the admission (I, C); long-term follow-up in complicated myocarditis (I, C).
AHA 2021 (children): no competitive sports while inflammation is active. Athletes: once inflammatory and injury markers, ventricular function and heart failure have normalized, 24-hour Holter and exercise test no sooner than 3 to 6 months, before return to competition.
Laboratory tests (children)
Test
Finding
Source
Troponin I or T
Often very high when raised; not sensitive or specific enough for biopsy-proven disease AHA 2021: higher levels associated with ECMO use and mortality; not correlated with dysfunction or arrhythmia. JCS 2023 (children): detectable 3–5 h after onset, abnormal for about 7–10 days; a normal CK-MB does not exclude myocarditis. AdultACC 2024: some patients have a normal hs-cTn; a low hs-cTn rule-out is untested.
Commonly raised; reflect heart failure rather than myocarditis Associated with cardiac dysfunction, heart failure signs and the need for CPR or MCS; trending may be more useful than a single random sample, apart from screening at presentation (AHA 2021).
Myocardial genome in ≈45–50% of suspected cases; blood, stool or respiratory about one-third, poorly correlated AHA 2021: peripheral PCR should not replace myocardial PCR unless biopsy is not feasible; antibody titres and peripheral cultures are unreliable. Common targets: parvovirus B19, adenovirus, enteroviruses, Epstein-Barr virus, cytomegalovirus, human herpesvirus 6. Yields differ: JCS 2023 (children) 38% of biopsy specimens; ESC 2025 up to 67%, varying widely. ESC 2025: a positive biopsy PCR needs blood tested in parallel to exclude acute systemic infection; basic panel also includes blood count with eosinophils, renal function, electrolytes, TSH and liver tests (Table 9).
Children Sinus tachycardia, ST-T changes, T-wave inversion, ST elevation, low limb-lead QRS voltage, AV conduction delay, later Q waves; AV block, VT, VF, SVT or atrial flutter or fibrillation may be the first sign (AHA 2021).
New third-degree heart block: always rule out myocarditis (AHA 2021).
AHA 2021: ST changes may be diffuse or in a coronary distribution; PR depression with pericarditis.
ESC 2025, citing mainly adult cohorts (Ammirati 2018, median age 34 y; Younis 2020, mean 37 y abstract): in acute myocarditis the ECG is normal in about 15%, ST elevation 57.5%, other ST/T changes 23.5%, conduction blocks 10%; QRS >120 ms on the first ECG is associated with death or transplant; a normal ECG does not exclude it.
AdultACC 2024: sensitivity 47%; pathological Q waves, LBBB, QRS ≥120 ms, long QT, high-grade AV block, malignant tachyarrhythmias, fragmented QRS and T-wave inversion are often associated with lower LV function, LV scar and worse prognosis; conduction disease raises suspicion of sarcoidosis, giant cell myocarditis or Lyme disease.
Echocardiography
Children First-line: global or regional LV or RV dysfunction, variable LV enlargement, edematous thick walls, effusion, thrombus, functional valve regurgitation (AHA 2021). ESC 2025: standard TTE with speckle tracking or tissue Doppler at presentation; GLS and GCS can be reduced with a preserved EF. AHA 2021: tissue Doppler and strain detect subtler changes; LV end-diastolic dimension and the severity of dysfunction are associated with outcome.
Supportive: LV dysfunction and wall thickness out of proportion to LV dilation (AHA 2021).
Fulminant pattern differs.JCS 2023 (children): thick walls despite mild dilation suggest it. ESC 2025: most children with it (usually <2 y) have a dilated, dysfunctional LV. AHA 2020 (fulminant): normal LV diastolic dimension with increased wall thickness; in children, smaller LV dimension and greater wall thickness are associated with better outcomes. AdultACC 2024: smaller cavity and mildly increased wall thickness.
Cardiac MRI: updated Lake Louise Criteria (2018)
Ferreira 2018 Table 3 “Regional” means at least 10 contiguous pixels. Published or local normal values, LV coverage and proper analysis tools must be acknowledged. Paired with LGE, the area of T1 abnormality should be beyond that seen on LGE. The T2 signal ratio is measured against skeletal muscle (serratus anterior if accessible); skeletal muscle inflammation can give a false-negative ratio. Original 2009 criteria: any 2 of 3 (T2-weighted, EGE ratio ≥4.0 or a 45% relative increase, LGE). The criteria apply only to suspected active or acute inflammation.
Criterion
Positive if any of
Target
T2-based (main)
Regional high T2 signal intensity (SI); global T2 SI ratio ≥2.0 on T2-weighted images; regional or global increase in myocardial T2 relaxation time
Myocardial edema
T1-based (main)
Regional or global increase in native T1 or ECV; high SI in a nonischemic pattern on LGE
Edema, hyperemia or capillary leak, necrosis, fibrosis
Supportive
Pericardial effusion on cine; high pericardial signal on LGE, T1 or T2 mapping
Pericardial inflammation
Supportive
Systolic LV wall motion abnormality on cine
LV dysfunction
Both: strong evidence of acute inflammation if pre-test probability is significant (ESC 2025: CMR-proven); one may still support it, less specifically (CMR-uncertain).
Typical LGE: patchy subepicardial and midwall, basal to mid-inferolateral. Ferreira 2018: severe cases may reach the subendocardium; hypereosinophilia: circumferential subendocardial LGE outside a coronary territory; giant cell: large areas, sometimes subendocardial; LGE alone cannot date an episode and is not recommended in isolation. ESC 2025: mid-wall anteroseptal LGE is associated with higher mortality and ventricular arrhythmia even with preserved LVEF. AdultACC 2024: ring-like midwall or subepicardial LGE in desmoplakin and other genetic cardiomyopathies.
Timing differs: best within 2 weeks (ESC 2025); in children LGE often appears ≥2 weeks after onset (JCS 2023). AdultACC 2024: first 1 to 2 weeks. JCS 2023: cardiac MRI within 2–3 weeks of onset.
In children
AHA 2021 describes the original 2009 Lake Louise criteria as an adult consensus and pediatric experience as limited (small single-center studies, varied scanners and protocols); Ferreira 2018 states no age limit and has a short pediatric section. In children CMR mainly identifies myocardial injury and separates myocarditis from noninflammatory cardiomyopathy. ESC 2025 applies its CMR-based approach to children.
Mapping values (especially ECV) depend on scanner, contrast agent, dose and protocol; centers should check whether published normal values apply and may need their own (AHA 2021). SCMR 2017: local reference range as mean ± 2 SD; without one, do not report native T1 or T2 values clinically; whether adult mapping experience applies to children is unclear.
AHA 2021 cites a study of 23 patients with clinically suspected myocarditis (Cornicelli 2019: acute myocarditis, under 21 y, median 15.2 y, range 0.6–18.8, retrospective, one center): raised T1, T2 and ECV, sensitivity 86–91%, specificity 74–89%; LGE 86%, T2-weighted signal 57%, hyperemia 13%. Banka 2015: 143 patients under 21 y, median 16.0 y, range 0.1–20.3, 13 hospitals, retrospective: LGE abnormal 81%, T2-weighted 74%, EGE 55%; read as positive in 82%. ESC 2025: children with fulminant myocarditis are usually under 2 y.
Feasibility: patient size, stability for transport and sedation, local expertise, no contraindication to gadolinium (AHA 2021 Figure 3). CMR is feasible in intubated patients (ESC 2025). JCS 2023 calls cardiac MRI preferable to biopsy, especially in children.
Persistent edema or fibrosis is not uncommon in children; its prognostic meaning is uncertain (AHA 2021).
CT and nuclear imaging
Children CT and radionuclide studies: not routinely recommended; coronary CT angiography if features overlap with an acute coronary syndrome (AHA 2021).
Nuclear imaging differs: ESC 2025 FDG-PET IIa; JCS 2023 children III (No benefit). ESC 2025: FDG-PET is an alternative when CMR is unsuitable (irregular rhythm, device artefact); preparation: high-fat, low-carbohydrate diet for 12–24 h, then fasting except water for 6–12 h before FDG. JCS 2023 discusses gallium and pyrophosphate scans: not recommended, particularly in infants; late contrast-enhanced CT helps when myocardial infarction must be excluded. AHA 2021: nuclear accuracy variable and generally low; radiation exposure.
Endomyocardial biopsy
Reference standard, but disease is focal, often in the LV free wall: a negative biopsy does not exclude it (AHA 2021).
Class differs: ESC 2025 I (high risk); JCS 2023 IIa children, IIb neonates.
Children Complications about 5% in some studies, up to 30% under 1 year or with LV biopsy (ESC 2025).
What the biopsy should include
Confirming features: lymphocytic infiltrate on histology or immunohistochemistry; myocyte injury or necrosis; positive viral PCR (AHA 2021 Figure 3). Dallas criteria alone: sampling error >25%.
ESC 2025: Table 11: at least 3 samples for histology and for immunohistology (CD3+ T lymphocytes, CD68+ macrophages, HLA-DR expression), plus PCR of myocardium and blood. ≥14 leucocytes/mm² with ≥7 CD3+ T cells/mm² has been the cut-off (Table 5 prints >7/mm²), now questioned by cardiac pathologists.
AdultACC 2024: higher yield early (within 2–4 weeks), ≥3 samples of 1–2 mm, voltage guidance; major complications <1% and minor 5–6% in experienced centers; risk is generally higher in children.
Red flags and fulminant myocarditis
Fulminant: acute onset, haemodynamically unstable, needing inotropes or mechanical circulatory support (ESC 2025 Table 3). AHA 2021 (children): presents as cardiogenic shock; tachyarrhythmias common. ESC 2025 complicated myocarditis: acute myocarditis with LVEF <50% on echo, sustained ventricular arrhythmias, advanced heart block, heart failure or cardiogenic shock. AdultACC 2024 stage D: inotropes, vasopressors or temporary circulatory support, or electrical instability needing intervention (high-grade AV block, frequent salvos of multifocal PVCs or NSVT, VT, VF).
AdultsChildren Risk: ESC 2025 Table 7 ESC 2025 proposes its approach in adults; §12.2.1 says the diagnostic approach applies also to children, and §16 calls the uncertainties especially pronounced in children. Table 7 guides the work-up and feeds the Figure 5 diagnostic algorithm, so it is shown with the diagnostic approach; its thresholds are not restated for children. Its footnote, read at the limit of legibility on the published image: footnoted high-risk items (arrest or syncope, VF or sustained VT, high-level AV block, LVEF <40%, extensive LGE) do not lead directly to biopsy; decide case by case. As printed, LVEF 40% falls in neither band; the text calls heart failure with LVEF ≤40% high risk. Admission (Recommendation Table 1): moderate to high risk, I, C; low risk, should be considered, IIa, C.
Risk
Clinical
Imaging
High
Acute heart failure or cardiogenic shock; NYHA III–IV dyspnoea refractory to therapy; cardiac arrest or syncope; VF or sustained VT; high-level AV block
Newly reduced LVEF <40%; extensive LGE
Intermediate
New or progressive dyspnoea; non-sustained ventricular arrhythmias; persistent or relapsing troponin release
Newly mildly reduced LVEF 41–49% and/or wall motion abnormality; LVEF ≥50% with LGE in ≥2 segments
Low
Stable or oligosymptomatic
LVEF ≥50%, no LGE or LGE <2 segments
Children Can worsen fast, even with borderline function: continuous rhythm monitoring, ICU decision, consider transfer to a pediatric MCS and transplantation center if heading toward compromise (AHA 2021). AHA 2021: especially with arrhythmia; in a registry 23% needed ECMO or a VAD early in the admission. ESC 2025Adult: Shock Team discussion with haemodynamic compromise (I, C); temporary MCS in cardiogenic shock (IIa, C). AHA 2020 Table 1: shock, electrical instability or rapidly evolving conduction abnormalities (QRS widening, PR prolongation); narrow pulse pressure, sinus tachycardia, cool or mottled extremities, raised lactate; right heart failure mistaken for hepatobiliary disease; fever may mimic sepsis. Avoid rate control of sinus tachycardia and avoid NSAIDs.
Children MCS for fulminant myocarditis with shock or life-threatening arrhythmia: IC (JCS 2023 Table 46).
Neonates VA-ECMO for fulminant myocarditis: IC (JCS 2023 Table 43).
Key points
Suspect it: new dysfunction plus viral prodrome, chest pain, ST-T changes, arrhythmia or raised troponin; new complete heart block.
Confirm with CMR (T2-based plus T1-based criterion) or biopsy; negatives do not exclude it.
Children (JCS 2023): troponin, echo, cardiac MRI (I); biopsy (IIa); nuclear imaging III (No benefit).
High risk (ESC 2025, adults and children): shock, sustained VT or VF, high-level AV block, newly reduced LVEF <40%. Heading toward compromise: consider transfer to a pediatric MCS and transplantation center (AHA 2021).
Law YM, Lal AK, Chen S, et al.; AHA Pediatric Heart Failure and Transplantation Committee of the Council on Lifelong Congenital Heart Disease and Heart Health in the Young and Stroke Council. Diagnosis and management of myocarditis in children: a scientific statement from the American Heart Association. Circulation 2021;144(6):e123-e135. doi:10.1161/CIR.0000000000001001. Archived publisher copy, corrected version; Figures 1 and 3 read from the page images. No classes of recommendation. Data Supplement (causes, CMR parameter table) not read.
Correction to: Diagnosis and management of myocarditis in children: a scientific statement from the American Heart Association. Circulation 2021;144(6):e149. doi:10.1161/CIR.0000000000001011. Sudden death in young athletes 6%, not 9%; table entry now not estimable.
Nagai T, Inomata T, Kohno T, et al. JCS 2023 guideline on the diagnosis and treatment of myocarditis. Circ J 2023;87(5):674-754. doi:10.1253/circj.CJ-22-0696. Open access. Covers adults, children and neonates; the pediatric (Tables 44-46) and neonatal (Tables 42-43) chapters are used here. Classes I, IIa, IIb, III (No benefit, Harm); levels A-C.
Schulz-Menger J, Collini V, Gröschel J, Adler Y, et al. 2025 ESC Guidelines for the management of myocarditis and pericarditis. Eur Heart J 2025;46(40):3952-4041. doi:10.1093/eurheartj/ehaf192. Archived publisher copy; recommendation tables, Table 7 and figures read from their images. Classes I, IIa, IIb, III; levels A-C. Its §12.2.1 states that the diagnostic approach applies also to children.
Ferreira VM, Schulz-Menger J, Holmvang G, et al. Cardiovascular magnetic resonance in nonischemic myocardial inflammation: expert recommendations. J Am Coll Cardiol 2018;72(24):3158-3176. doi:10.1016/j.jacc.2018.09.072. Archived publisher copy. Expert recommendations, no classes; the updated Lake Louise Criteria are its Table 3.
Drazner MH, Bozkurt B, Cooper LT, et al. 2024 ACC Expert Consensus Decision Pathway on strategies and criteria for the diagnosis and management of myocarditis. J Am Coll Cardiol 2025;85(4):391-431. doi:10.1016/j.jacc.2024.10.080. Archived publisher copy, text only. Its stated focus is adults (refers to AHA 2021 for children): labelled Adult. No classes of its own.
Kociol RD, Cooper LT, Fang JC, et al. Recognition and initial management of fulminant myocarditis: a scientific statement from the American Heart Association. Circulation 2020;141(6):e69-e92. doi:10.1161/CIR.0000000000000745. Archived publisher copy. Not limited to children; no classes of its own.
Messroghli DR, Moon JC, Ferreira VM, et al. Clinical recommendations for cardiovascular magnetic resonance mapping of T1, T2, T2* and extracellular volume: a consensus statement by the Society for Cardiovascular Magnetic Resonance (SCMR) endorsed by the European Association for Cardiovascular Imaging (EACVI). J Cardiovasc Magn Reson 2017;19:75. doi:10.1186/s12968-017-0389-8. Open access (PMC5633041); the SCMR document AHA 2021 cites.
Cornicelli MD, Rigsby CK, Rychlik K, et al. Diagnostic performance of cardiovascular magnetic resonance native T1 and T2 mapping in pediatric patients with acute myocarditis. J Cardiovasc Magn Reson 2019;21:40. doi:10.1186/s12968-019-0550-7. Open access (PMC6631973). Its cut-offs are scanner-specific and not shown.
Banka P, Robinson JD, Uppu SC, et al. Cardiovascular magnetic resonance techniques and findings in children with myocarditis: a multicenter retrospective study. J Cardiovasc Magn Reson 2015;17:96. doi:10.1186/s12968-015-0201-6. Open access (PMC4650339).
Abstracts only
Ammirati E, Cipriani M, Moro C, et al. Clinical presentation and outcome in a contemporary cohort of patients with acute myocarditis: Multicenter Lombardy Registry. Circulation 2018;138(11):1088-1099. doi:10.1161/CIRCULATIONAHA.118.035319. Cited by ESC 2025 for its ECG percentages; age from the abstract.
Younis A, Matetzky S, Mulla W, et al. Epidemiology characteristics and outcome of patients with clinically diagnosed acute myocarditis. Am J Med 2020;133(4):492-499. doi:10.1016/j.amjmed.2019.10.015. Cited by ESC 2025 for its ECG percentages; age from the abstract.
How it was checked
Criteria, thresholds, classes and levels are copied from the sources (October 2026); wording is condensed. Names and abbreviations follow each source (updated Lake Louise Criteria, CMR, EMB, LGE, EGE, ECV, SI, MCS). JCS and ESC rows keep their own class labels; AHA 2021, Ferreira 2018, ACC 2024 and AHA 2020 give no classes.
ESC 2025 proposes its approach in adults; its §12.2.1 says the diagnostic approach applies also to children, so its diagnostic rows and its Table 7 risk grades (which feed the Figure 5 diagnostic algorithm) carry Adults and Children chips, and its other rows (Shock Team, circulatory support, genetic testing, follow-up) are labelled Adults. §16 calls the uncertainties especially pronounced in children. ACC 2024 is labelled Adult. AHA 2021 describes the original 2009 Lake Louise criteria as an adult consensus; Ferreira 2018 states no age limit.
Differences between sources, as printed: fulminant echo pattern in children (JCS 2023 thick walls with mild dilation; ESC 2025 dilation in most young children); nuclear imaging (ESC 2025: FDG-PET IIa; JCS 2023: nuclear imaging III in children); biopsy class (ESC 2025 I in high risk; JCS 2023 IIa children, IIb neonates); timing of CMR (ESC 2025 first 2 weeks, ACC 2024 (Adult) 1–2 weeks, JCS 2023 2–3 weeks); viral genome yield (AHA 2021 ≈45–50%, JCS 2023 38%, ESC 2025 up to 67%); ESC 2025 prints the T-cell cut-off as ≥7 in the text and >7 in its Table 5; JCS 2023 Table 44 restates the AHA 2021 frequencies with some different ranges, and calls the Banka 2015 study prospective, while its title says retrospective.
ESC 2025 Table 7 was read from a small image; the footnote was at the limit of legibility. The ages of the ESC 2025 ECG cohorts come from those studies’ abstracts.
Not covered on this page
Treatment (immunotherapy, antivirals, heart failure drugs), arrhythmia management and device decisions, multisystem inflammatory syndrome in children, vaccine-related myocarditis, and pericarditis.