We are presenting a case of endocarditis due to a penicillin-tolerant Streptococcus bovis in a 65-year-old patient. The minimal bactericidal concentration of penicillin (40 mg/l) was more than 100-fold the minimal inhibitory concentration (0.08 mg/l). The MBC of penicillin was 0.31 mg/l in the presence of 1.25 mg/l gentamicin. Cross-sectional echocardiography revealed endocarditis of the anterior leaflet of the tricuspid valve and a vegetation on the aortic valve which appeared to be pedunculated and which prolapsed into the left ventricular outflow tract during diastole. During therapy, the pedunculated part of the vegetation disappeared without signs of embolization. After initial clinical improvement, the patient died of cerebral bleeding caused by a mycotic aneurysm of the left median cerebral artery. The patient's final outcome suggested an asymptomatic embolus. Cross-sectional echocardiography was distinctly superior to M-mode echocardiography in estimating changes in the size and shape of the valve vegetation. The results of the post-mortem examination of the aortic and tricuspid valves corresponded to the echocardiographic findings.