We report the case of a patient with uterine myoma who developed uncontrollable massive hemorrhage from the uterus during anticoagulant therapy after cardiac valve replacement and required hysterectomy. There was a discrepancy between the laboratory findings regarding the blood coagulation system and the clinical manifestations, suggesting a combination of multiple factors, such as a hormonal imbalance. This was a case that demanded strict attention to the management of the uterine lesions during the conduct of anticoagulant treatment.