The ever-increasing use of immune checkpoint inhibitors in cancer is leading to a high incidence of autoimmune side effects. This report discusses an autoimmune fulminant myocarditis in an elderly patient with metastatic pulmonary adenocarcinoma in whom the most advanced invasive heart failure therapies were used successfully. She was treated with nivolumab. This case illustrates a severe cardiovascular complication of immunotherapy and highlights to cardiologists the importance of aggressive treatments in patients with metastatic cancers whose prognosis has improved dramatically.