OPTIMAL management of patients with rheumatic heart disease or a previous bout of acute rheumatic fever includes the administration of prophylactic antibiotics to prevent pharyngeal infection with Group A streptococci.1 , 2 Several studies have shown that oral penicillin prophylaxis is associated with a high prevalence of penicillin-resistant bacteria in the gingival flora.3 4 5 6 7 8 9 An original concern was that continuous low-dose prophylaxis would result in a high incidence of endocarditis due to resistant organisms that would be difficult to cure. Follow-up studies of large numbers of patients taking prophylactic penicillin have found no increase in the incidence of endocarditis,10 and few cases of . . .