The American Heart Association recently revised its guidelines for the prevention of bacterial endocarditis. These guidelines are meant to aid physicians, dentists and other health care providers, but they are not intended to define the standard of care or to serve as a substitute for clinical judgment. In the guidelines, cardiac conditions are stratified into high-, moderate- and negligible-risk categories based on the potential outcome if endocarditis develops. Procedures that may cause bacteremia and for which prophylaxis is recommended are clearly specified. In addition, an algorithm has been developed to more clearly define when prophylaxis is recommended in patients with mitral valve prolapse. For oral and dental procedures, the standard prophylactic regimen is a single dose of oral amoxicillin (2 g in adults and 50 mg per kg in children), but a follow-up dose is no longer recommended. Clindamycin and other alternatives are recommended for use in patients who are allergic to penicillin. For gastrointestinal and genitourinary procedures, the prophylactic regimens have been simplified. The new recommendations are meant to more clearly define when prophylaxis is or is not recommended, to improve compliance, to reduce cost and the incidence of gastrointestinal side effects, and to approach more uniform worldwide recommendations.