These changes are intended to define more clearly when infective endocarditis prophylaxis is or is not recommended and to provide more uniform and consistent global recommendations. (Circulation. 2007;116:1736-1754.) Key Words: AHA Scientific Statements cardiovascular diseases endocarditis prevention antibiotic prophylaxis Infective endocarditis (IE) is an uncommon but life- threatening infection. Despite advances in diagnosis, antimi- crobial therapy, surgical techniques, and management of com- plications, patients with IE still have high morbidity and mortality rates related to this condition. Since the last American Heart Association (AHA) publication on prevention of IE in 1997,1 many authorities and societies, as well as the conclusions of published studies, have questioned the efficacy of antimicro- bial prophylaxis to prevent IE in patients who undergo a dental, gastrointestinal (GI), or genitourinary (GU) tract procedure and have suggested that the AHA guidelines should be revised.2 5 Members of the Rheumatic Fever, Endocarditis, and Kawasaki Disease Committee of the AHA Council on Cardiovascular Disease in the Young ( the Committee ) and a national and international group of experts on IE extensively reviewed data published on the prevention of IE. The Committee is especially grateful to a group of international experts on IE who provided content review and input on this document (see Acknowledg- ments). The revised guidelines for IE prophylaxis are the subject of this report. The writing group was charged with the task of perform- ing an assessment of the evidence and giving a classifica- tion of recommendations and a level of evidence (LOE) to each recommendation. The American College of Cardiol- ogy (ACC)/AHA classification system was used as follows. Classification of Recommendations: Class I: Conditions for which there is evidence and/or general agreement that a given procedure or treatment is beneficial, useful, and effective. 