Myocarditis is a complex inflammatory disease, usually occurring secondary to viral infections, autoimmune processes or toxic agents. Clinical presentations are multiple, including chest-pain, heart failure and a broad spectrum of arrhythmias. In turn, outcome is largely unpredictable, ranging from mild self-limiting disease, to chronic stage and progressive evolution towards dilated cardiomyopathy, to rapid adverse outcome in fulminant forms. Subsequently, myocarditis is often underdiagnosed and undertreated, and optimal diagnostic and therapeutic strategies are still to be defined. This study, both retrospective and prospective, originally single-center and subsequently upgraded to multicenter, aims at answering multiple questions about myocarditis, with special attention to its arrhythmic manifestations. 1. Optimal diagnostic workflow is still to be defined. In fact, although endomyocardial biopsy (EMB) is still the diagnostic gold standard, especially for aetiology identification, it is an invasive technique. Furthermore, it may lack sensitivity because of sampling errors. By converse, modern imaging techniques - cardiac magnetic resonance (CMR) in particular - have been proposed as alternative or complementary diagnostic tool in inflammatory heart disease. Other noninvasive diagnostic techniques, like delayed-enhanced CT (DECT) scan or position emission tomography (PET) scan, are under investigation. 2. Biomarkers to identify myocarditis aetiology, predisposition, prognosis and response to treatment are still to be defined. 3. Arrhythmic myocarditis is largely underdiagnosed and uninvestigated. Importantly, myocarditis presenting with arrhythmias requires specific diagnostic, prognostic and therapeutic considerations. At the group leader hospital, which is an international referral center for ventricular arrhythmias management and ablation, a relevant number of patients with unexplained arrhythmias had myocarditis as underlying aetiology. The experience of a dedicated third-level center is going to be shared with other centers, to considerably improve knowledge and management of arrhythmic myocarditis. 4. The role of CMR, as well as alternative noninvasive imaging techniques, in defining myocarditis healing is a relevant issue. In particular, optimal timing for follow-up diagnostic reassessment is still to be defined, in patients with myocarditis at different inflammatory stages, either with or without aetiology-dependent treatment. 5. Uniformly-designed studies are lacking, to compare myocarditis among different patient subgroups, differing by variables like: clinical presentations, myocarditis stage, associated cardiac or extra-cardiac diseases, aetiology-based treatment, associated arrhythmic manifestations, diagnostic workup, and devices or ablation treatment.