In this retrospective study, they reported 140 episodes of suspected myocarditis (49 confirmed, 91 probable) in 26 centers. Most patients were men (n=126, 90.6%), the median age was 15.8 years ([12.1-20.3]; [IQR], 14.5-17.0 ). Suspected myocarditis occurred in 136 patients (97.8%) after the mRNA vaccine, with 131 (94.2%) after the Pfizer-BioNTech vaccine; 128 (91.4%) occurred after the second dose. Symptoms began a median of 2 days (range, 0-22; IQR, 1-3) after vaccination. The most frequent symptom was chest pain (99.3%). Most cases of suspected COVID-19 vaccine myocarditis that occurred in persons <21 years of age had a mild clinical course with rapid resolution of symptoms.