Twenty‐one patients (60%) were classified as severe myocarditis, and they presented higher cardiac troponin I (cTnI) levels (p = 0.013), higher N‐terminal pro‐B‐type natriuretic peptide levels (p = 0.031), higher creatine kinase levels (p = 0.018), higher CK‐MB levels (p = 0.026), and higher neutrophil to lymphocyte ratio (NLR) levels (p = 0.016) compared to non‐severe myocarditis patients after ICI treatment. This evidence concerns the gene TNNI3 and myocarditis.