We report a case of fatal immune checkpoint inhibitor (ICI)-associated myocarditis in a 77-year-old man with metastatic non-small cell lung cancer (NSCLC) who presented for mediport placement at our outpatient surgical center. He denied any cardiac complaints and had a previously normal electrocardiogram (EKG) off treatment. Intraoperatively and postoperatively, he displayed cardiac rhythm abnormalities. The patient was then transferred to a tertiary facility, where he expired within 48 hours. As cancer immunotherapy becomes increasingly prominent, ICI-associated myocarditis should be considered a potentially critical contributor to perioperative cardiac morbidity and mortality.