The incidence of endocarditis due to Cardiobacterium hominis is probably underestimated because clinical presentations vary greatly and culture of this Gram negative germ is difficult. A 48-year-old man with a past history of post-streptococcic aortic regurgitation was hospitalized twice within 1 week for fever (38 degrees C) and junctional tachycardia which responded to amiodarone. Subsequently, infero-apical necrosis was documented. Based on the result of the laboratory tests, coronary embolism was suspected although 12 blood cultures were negative. The patient recovered well with a standard antibiotic treatment. Fifteen days later, the blood cultures revealed Cardiobacterium hominis. Antibiotic therapy was adapted and aortic valve replacement was programmed. Two months later the patient died from uncontrollable left heart failure. A 63-year-old man who had had mitral valve replacement 10 years earlier for Streptococcus mitis endocarditis was hospitalized for fever (38 degrees C) and a painful left calf. Phlebocavography eliminated deep vein thrombosis and a complete cardiac work-up was inconclusive. Endocarditis was suspected although blood cultures were negative. The patient was given oral penicillin and discharged after one week. Three months later, the patient was again febrile (38 degrees C) and suffered a cerebral vascular event. Fourteen days after blood sampling, cultures revealed Cardiobacterium hominis. The patient's haemodynamic status worsened and valve replacement with atrioplasty was performed. Outcome after 4 years follow-up has been favourable. Endocarditis due to Cardiobacterium hominis, a saprophitic germ of the upper airway and the female genital tract, has been reported in 64 cases in the literature. The clinical picture is often limited to fever and a heart murmur and laboratory tests show an accelerated erythrocyte sedimentation rate and hyperleukocytosis. Inflammatory type anaemia is often found due to the latency of the endocarditis. Complications are frequent and can be fatal due to massive pulmonary emboli, cerebral vascular events or irreversible heart failure. C. hominis is sensitive to amoxycillin and netilmicin. Surgical treatment of the valvulopathy is indicated.