Fifty hospitalized consecutive patients with clinically suspected myocarditis (MC) who meet the inclusion/exclusion criteria will be enrolled to the study.

During index hospitalization patients will undergo a standard clinical evaluation (physical examination, collection of a medical history, blood tests (including troponin, N-terminal-pro Brain Natriuretic Peptide (NTproBNP), C-reactive protein (CRP), Suppression of Tumorigenicity 2 (ST2), Galectin-3), 24-h Holter ECG, echo, coronary angiography, magnetic resonance imaging (MRI)). Women of childbearing potential will undergo a pregnancy test prior to radiological examinations. After signing the informed consent patients will undergo resting single photon emission computed tomography (SPECT) to assess possible myocardial perfusion defects and then 18F-2-fluoro-2-deoxy-D-glucose fluorodeoxyglucose positron emission tomography/computed tomography FDG-PET/CT. After MRI and FDG-PET/CT tests patients will undergo right ventricular endomyocardial biopsy (EMB) (5-8 myocardial tissue samples). Blood biomarkers of fibrosis and myocardial necrosis, as well as anticardiac autoantibodies will be evaluated at baseline and after 3 months (serum will be stored at -80 °C for final evaluation). After 3-months from enrollment follow-up visit will be performed with clinical evaluation. All patients will undergo physical examination, collection of a medical history, blood tests, 24-h Holter ECG, echo, MRI.

Fifty hospitalized consecutive patients with clinically suspected MC who meet the inclusion/exclusion criteria will be enrolled to the study.

During index hospitalization patients will undergo a standard clinical evaluation (physical examination, collection of a medical history, blood tests (including troponin, N-terminal-pro Brain Natriuretic Peptide (NTproBNP), C-reactive protein (CRP), Suppression of Tumorigenicity 2 (ST2), Galectin-3), 24-h Holter ECG, echo, coronary angiography, MRI). Women of childbearing potential will undergo a pregnancy test prior to radiological examinations. After signing the informed consent patients will undergo resting single photon emission computed tomography (SPECT) to assess possible myocardial perfusion defects and then cardiac FDG-PET/CT. After MRI and FDG-PET/CT tests patients will undergo right ventricular EMB (5-8 myocardial tissue samples). Blood biomarkers of fibrosis and myocardial necrosis, as well as anti-heart autoantibodies will be evaluated at baseline and after 3 months (serum will be stored at -80 °C for final evaluation). After 3-months from enrollment follow-up visit will be performed with clinical evaluation. All patients will undergo physical examination, collection of a medical history, blood tests, 24-h Holter ECG, echo, MRI.

FDG-PET/CT imaging Resting SPECT will be performed one day before the FDG-PET/CT examination. Physiological glucose uptake in the myocardium will be suppressed using dietary preparation (low-carbohydrate high-fatty diet). 48 h before the FDG-PET/CT examination, all patients' meals will be low-carbohydrate. 24 h before the FDG-PET/CT examination (the "SPECT day"), breakfast and dinner (last meal at 4:00 PM) will be high-fat, then fasting (a patient should drink only still water) until FDG-PET/CT examination in the next morning (9:00 PM). Single-dose heparin will be administered intravenously at a low dose (50 IU/kg) 15 minutes before the start of the FDG-PET/CT examination to increase the accuracy of the test. Capillary blood glucose level will be measured 20 minutes before the FDG-PET/CT examination.

Because of radiation, for about 6 h after the scan patients should avoid contact with children and pregnant women.

Inclusion Criteria:

• Signed informed consent (including consent for MRI, FDG-PET/CT and EMB)
• Age ≥18 years
• Clinically suspected MC (according to the 2013 Criteria of the ESC Working Group on Myocardial and Pericardial Diseases)
• Symptoms associated with MC with a duration of <6 months
• Women of childbearing potential must have a negative urine or blood pregnancy test

Exclusion Criteria:

• Pregnancy or lactation
• Any contraindication or intolerance to MRI or PET investigations (including but not limited to: presence of pacemakers not compatible with MRI, aneurysm clips, artificial heart valves, ear implants, or foreign metal objects in the eyes, skin, or body that would contraindicate an MRI scan)
• Subjects with body mass index >45 kg/m2
• Active neoplasm or diagnosed sarcoidosis

50 patients with suspected myocarditis

External requests for study data will be granted, however, any information that is shared will be blinded to any identifying participant information.

after end of the study

External requests accepted by the study investigators