The 1984 recom- mendations attempted to simplify prophylactic regimens by providing clear lists of procedures for which prophy- laxis was and was not recommended and reduced postpro- cedure prophylaxis for dental, GI, and GU tract procedures to only 1 oral or parenteral dose.12 In 1990, a more complete list of cardiac conditions and dental or surgical procedures for which prophylaxis was and was not recom- mended was provided.13 These previous recommendations rec- ognized the potential medical-legal risks associated with IE prophylaxis and suggested that the recommendations were Wilson et al Prevention of Infective Endocarditis 1737 intended to serve as a guideline, not as established standard of care. The most recent AHA document on IE prophylaxis was published in 1997.1 The 1997 document stratified cardiac conditions into high-, moderate-, and low-risk (negligible risk) categories, with prophylaxis not recommended for the low-risk group.1 An even more detailed list of dental, respi- ratory, GI, and GU tract procedures for which prophylaxis was and was not recommended was provided. The 1997 document was notable for its acknowledgment that most cases of IE are not attributable to an invasive procedure but rather are the result of randomly occurring bacteremias from routine daily activities and for its acknowledgment of possi- ble IE prophylaxis failures. Rationale for Revising the 1997 Document It is clear from the above chronology that the AHA guidelines for IE prophylaxis have been in a process of evolution more than 50 years. The rationale for prophylaxis was based largely on expert opinion and what seemed to be a rational and prudent attempt to prevent a life-threatening infection. 