Background MessengerRNA (mRNA) COVID–19 vaccination has been associated with a higher–than–expected occurrence of acute myocarditis. Scarce information is available on mid–term prognosis and changes in cardiac function, volumes, and tissue characterization on cardiac magnetic resonance (CMR). Methods Retrospective, multicenter study including patients with a definite diagnosis of acute myocarditis within 30 days from mRNA COVID–19 vaccination. The diagnosis is based on endomyocardial biopsy (EMB) or autopsy or by the coexistence of positive biomarkers (troponin >99th upper reference limit or elevated creatine kinase myocardial band [CK–MB]) and cardiac MRI findings consistent with AM according to the 2018 updated Lake Louise Criteria. Results 77 patients (median age 25 years [IQR 20–35], 15% female) were included and followed–up for 147 days [IQR 74–215]. Follow–up CMR was available in n=49 patients and showed no changes in biventricular ejection fraction (EF) as compared to CMR at diagnosis (left ventricular EF: 59%[55–65]vs. 60%[57–64], p=0.507, right ventricular EF: 56%[52–62]vs. 57%[52–61], p=0.563, respectively). Late gadolinium enhancement was present in all patients at diagnosis and persisted in only n=39 (79.6%) at follow–up (p=0.001), generally sparing the anterior wall and the septum. N=10 (20.4%) had a persistent edema based on T2–weighted short tau inversion recovery (STIR) sequences, with predominant involvement of inferior or inferior–lateral walls. The proportion of patients with increased T1 and T2 mapping signals significantly decreased at follow–up (n=13 (68%) vs. n=4 (13%),p<0.001, and n=21 (84%) vs. n=3 (10%),p<0.001, respectively), as well as the presence of pericardial effusion (n=16 (33%) vs. n=3 (6%),p=0.004). No differences in morpho–functional CMR parameters based on the type of vaccine administered were found (BNT162b2 Pfizer/BioNTech®, n=36, 73.5%, m–RNA–1273 Moderna®, n=13, 26.5%). Among patients with available follow–up (N=75, 97.4%), no major adverse cardiovascular events nor myocarditis recurrence or death were reported. Conclusions At mid–term follow–up, patients who experienced an acute myocarditis after a mRNA COVID–19 vaccine had preserved biventricular EF. The rate and localization of residual scar or edema on CMR is in line with classic viral myocarditis with a good prognosis. This new piece of information should further reassure patients who experience acute myocarditis after mRNA COVID–19 vaccination.