Abstract： A 64-year-old female patient received a 3-week treatment regimen of sintilimab(200 mg,d1),oxaliplatin(200 mg,d1)and tegafur gimercil and oteracil porassium capsule(60 mg,bid,d1～14)for gastric cardia adenocarcinoma.On the 7th day of the second cycle of treatment,the patient developed backache.Laboratory tests showed abnormal cardiac biomarkers.ECG presented abnormal Q waves in leads Ⅲ and aVF,and flat T waves.After excluded from atherosclerosis-in-duced coronary artery disease via coronary CT scan,the patient was then diagnosed with immune-related myocarditis.The an-ti-cancer drugs were discontinued,and the patient was treated with methylprednisolone for 9 days,after which the symptoms relieved and the values of cardiac injury markers significantly decreased.Myocarditis is a rare and severe adverse effect of sin-tilimab,thus clinicians should closely monitor changes in cardiac injury markers and symptoms in patients receiving this drug.