We report a 20-year-old male patient with preoperatively undiagnosed myocarditis, who received general anesthesia for laparoscopic appendectomy. Because of arrhythmia, a cardiologist was consulted postoperatively. The 12-lead electrocardiogram showed complete atrioventricular block and the echocardiogram showed global hypokinesia of the left ventricle with impaired contractility, a left ejection fraction of 37%, and a dilated right heart. Subsequently, a permanent pacemaker was implanted and the patient was discharged from hospital without any complications.