A 74-year-old man with lung adenocarcinoma recurrence was admitted to our hospital because of dyspnea 7 days after receiving initial immunotherapy with nivolumab. Electrocardiography revealed ST-segment elevation in V1-6 and echocardiography showed a markedly reduced left ventricular ejection fraction of 9% and akinesis of the anteroseptal wall and apex. He died from acute heart failure 3 days after admission. Microscopically, multiple small foci of myocardial necrosis with few inflammatory cells were scattered in both ventricles. Obstruction of the coronary artery was not identified. We believed that the cause of death was acute heart failure possibly due to nivolumab-induced myocardial necrosis.