BACKGROUND: The presence of late gadolinium enhancement (LGE) at cardiac magnetic resonance (CMR) has diagnostic and prognostic value in patients with acute myocarditis (AM). Aim of our study was to quantify the changes in LGE extension (LGE%) early after AM and evaluate its relations with biventricular function and morphology. METHODS: We investigated 76 consecutive patients with AM (acute onset of chest pain/heart failure/ventricular arrhythmias not explained by other causes, and raised troponin) that met CMR criteria based on myocardial oedema at T2-weighted images and LGE on post-contrast images at median time of 6days from onset of symptoms. We quantified LGE% at baseline and after 148days in 49 patients. RESULTS: Median left ventricular (LV)-ejection fraction (EF) was 64% (interquartile range [Q1-Q3]: 56-67%), and LGE% 9.4% (Q1-Q3: 7.5-13.2%). LGE% was correlated with LV end-systolic volume index (LV-ESVi; r=+0.34; p=0.003). LGE% was inversely correlated with LV-EF (r=-0.31; p=0.009) and time to CMR scan (r=-0.25; p=0.028). In the 49 patients with a second CMR scan, despite no significant variations in LV-EF, a significant decrease of LGE% was observed (p