Streptococcus agalactiae infective endocarditis Streptococcus agalactiae is an unusual cause of infectious endocarditis. We describe the clinical characteristics, therapy and evolution of this infection in four patients diagnosed between 1996 and 2003. All four cases had native valve involvement and vegetations. All the patients had severe aortic failure and three of them also developed heart failure. Valve replacement surgery was performed in all four cases. Mortality was 50%. Infectious endocarditis due to S. agalactiae is very aggressive. Early surgery should be considered to prevent valve destruction and serious complications.