Introduction: Myocarditis in children still poses diagnostic difficulties. Aim of the paper: Assessment of the course of myocarditis in children. Materials and methods: Retrospective study (2009–2019) included 81 patients with myocarditis with analysis of the clinical course, biomarker levels, electrocardiogram, echocardiography and magnetic resonance imaging. Results: The most frequently reported symptom of myocarditis was chest pain in 73 (90%) patients. In 66 (81.5%) patients, the serum troponin I concentration was above the norm (the sensitivity 81.5%), the mean 12,539 ± 11,394 ng/L. In 24 out of 25, the concentration of N-terminal pro-brain natriuretic peptide was above the limit (mean of 866 ± 976 pg/mL). 71 patients had an abnormal electrocardiogram (sensitivity 88%). In echocardiography, 23 (28%) patients had left ventricular ejection fraction below normal limit, the mean 64.5 ± 7.1%. In the subgroup of patients treated with an angiotensin converting enzyme inhibitor, an improvement in left ventricular ejection fraction and end-diastolic dimension was observed. In the subgroup of overweight and obese subjects, 93.3% of patients showed abnormalities in control cardiac magnetic resonance after 6 months, including 33.3% with signs of active inflammation. 60% patients in the subgroup with a body mass index <20 kg/m² had normal cardiac magnetic resonance imaging. Conclusion: Myocarditis course in adolescents is usually mild. In the overweight and obese patients the occurrence of the disease is more frequent and myocardial abnormalities last longer. The use of an angiotensin converting enzyme inhibitor improves the left ventricular systolic function and the end-diastolic dimension of the left ventricle in patients with myocarditis.