A 79-year-old woman, who had undergone mitral valve replacement with a Björk-Shiley valve 16 years previously, was transferred to our institute due to active prosthetic valve infection associated with severe heart failure on respirator. On admission, her white blood cells and c-reactive protein (CRP) were elevated to 15,700/µl and 7.29 mg/dl, respectively, and she had anemia (hemoglobine 8.1 g/dl), thrombocytopenia (platelets 75,000/µl), and renal dysfunction (blood urea nitrogen 57 mg/dl, creatinine 1.8 mg/dl, estimated glomerular filtration rate 21.5 ml/min/1.73 m²). Her brain natriuretic peptide was elevated to 456.7 pg/dl. Blood culture revealed bacteremia with Streptococcus agalactiae. Though CT scan revealed cerebellum infarction, we decided to perform emergency surgery because of uncontrollable infection and heart failure, even with massive infusion of catecholamine and respiratory support. At surgery, huge vegetation proliferated over the prosthetic valve. The prosthetic valve was detached from approximately two-thirds of the annulus due to an annular abscess. The infected annulus was resected aggressively. Mitral annulus was reconstructed and reinforced with a bovine pericardial patch, and the bioprosthetic valve of 23 mm in size was implanted in an intra-annular position. In the postoperative phase, antibiotics (ampicillin, gentamicin) was given, and CRP became negative 47 days postoperatively, and the patient discharged from the hospital 56 days after the operation.