Endocarditis due to Cardiobacterium hominis is rare and may be treated with a variety of antibiotics. We isolated the bacteria from blood cultures of a patient with Cardiobacterium hominis endocarditis who could be successfully treated with ciprofloxacin. The bacterial features of Cardiobacterium hominis are presented, and susceptibility to ciprofloxacin is documented with bacterial killing curves employing peak and trough specimens of patient's serum.