Abstract
Pembrolizumab, a humanized monoclonal IgG4 antibody directed against programmed death-1, is an immune checkpoint inhibitor that has been introduced for the treatment of non-small-cell lung cancer. However, immune checkpoint inhibitors may cause severe immune-related adverse events. We herein present a case of lung cancer with complete atrioventricular block associated with acute myocarditis, which developed 16 days after the administration of pembrolizumab. The clinical course of this case suggested a strong need for close cardiac monitoring when pembrolizumab is administered on an outpatient basis.