From February, 1975 through October, 1990, 26 patients underwent surgical treatment for infective endocarditis at Tokai University Hospital. The overall operative mortality rate was 11.5% (3/26). The three patients who died were suffering from aortic prosthetic valve endocarditis (PVE) in the active stage. Among 16 patients in the active stage, the mortality rate was 18.7% (3/16) Among 10 patients with native valve endocarditis (NVE) in the healed stage, all survived. Among the total of 21 patients with NVE, the mortality rate was zero and among those with PVE, the rate was 60% (3/5). Various species of streptococci were the most common organisms encountered, followed by Staphylococcus epidermides. The two PVE patients with S. epidermides died. Nine of the 11 NVE cases in the active stage were of the localized type. Only one case of the localized type of PVE suffered from an infected mitral bioprosthetic valve. The 6 extensive-type cases had aortic valve endocarditis (2NVE, 4PVE). Three patients with the extensive type of PVE died. We conclude that patients with infective endocarditis who develop progressive congestive heart failure, recurrent embolization, or progressive sepsis despite antimicrobial treatments, should undergo prompt valve replacement within 7 days after institution of therapy.