A 36-year-old female patient developed Cardiobacterium hominis endocarditis on a mitral valve prosthesis. The etiologic agent was identified in the seventh day of incubation of the blood cultures specimens. Crystalline penicillin (18.10(6) UI daily) and amikacin (800 mg daily) were administered for 42 days. Surgical treatment for heart failure unresponsive to medical treatment was carried on in the eighteenth day of antibiotic therapy. A bovine pericardium prosthesis was inserted. The patient was discharged and is asymptomatic after seven months.