A 61-year-old man was admitted to an associated hospital because of fever. He had undergone aortic valve and mitral valve replacement 6 years ago, because of rheumatic aortic valve stenosis, and mitral valve stenosis and regurgitation. He had prosthetic valve endocarditis caused by a rare Streptococcus constellatus infection complicated by multiple organ failure and systemic embolism. We considered that surgical treatment was difficult, and continued antibiotic treatment. The inflammatory reaction and fever improved. Prosthetic valve endocarditis is often difficult to identify and treat. Streptococcus constellatus infection is characterized by destruction and formation of abscess. We followed up the patient by transesophageal echocardiography, and observed the course of change of the paravalvular abscess around the aortic valve from echogenic to echolucent.