A 55-year-old male cancer patient with ICI therapy (PD-1 antibody) started to manifest myasthenia gravis (MG) symptoms, cardiac injury, intermittent third-degree atrioventricular block, and ventricular pause necessitating temporary cardiac pacing. Intravenous steroids and immunoglobulin, pyridostigmine, and mycophenolate mofetil were sequentially initiated and the above symptoms were gradually resolved.