Abstract
A 71-year-old Japanese woman was hospitalized for heart failure with Loeffler endocarditis, bronchial asthma, fever, and mononeuritis multiplex after receiving the fifth dose of the coronavirus disease 2019 (COVID-19) vaccine. Laboratory tests revealed eosinophilia and increased antineutrophil cytoplasmic antibody levels. The patient's condition improved after anticoagulant therapy. Loeffler endocarditis with antineutrophil cytoplasmic antibody-associated vasculitis may be associated with the COVID-19 vaccination.