Cardiobacterium hominis, a member of the HACEK group of organisms, is a rare cause of endocarditis. We report a case of infective endocarditis caused by C. hominis in a male child who had undergone right ventricular outflow tract (RVOT) reconstruction using an expanded polytetrafluoroethylene conduit for tetralogy of Fallot with pulmonary atresia. Two days before admission, the patient suffered from exertional shortness of breath. Right ventricular hypertension was confirmed and RVOT stenosis was suspected based on the echocardiography findings. A CT scan revealed vegetation above the cusp of the conduit. An emergency operation was performed to avoid a pulmonary embolism due to large friable vegetation. C. hominis was cultured from the blood and the vegetation, prompting a diagnosis of prosthetic valve endocarditis. The patient was discharged after a 6-week course of intravenous ceftriaxone therapy.