(1) Background: Myocarditis following group A streptococcal pharyngitis and tonsillitis is a relatively rare medical condition. The aim of this systematic review was to identify specific ECG changes, laboratory parameters and signs, and symptoms associated with this disease. (2) Methods: A systematic literature review was performed in concordance with the current PRISMA guidelines, including the databases PubMed/MEDLINE, Web of Science, CDSR, CENTRAL, CCAs, EBM Reviews, and LILACS.