Myocardial abscess caused by anaerobic infection is rare and usually occurs in cases of myocardial infarction, in which it may be related to areas of low oxygen tension. Bacteroides CDC group F-1 infective endocarditis complicated by an aortic valve ring abscess with resultant complete heart block developed in a patient with steroid dependent systemic lupus erythematosus. The genitourinary system was the presumed source of the infection. Endocarditis developed after an elective abortion, despite antibiotic prophylaxis according to American Heart Association recommendations. This case shows that an anaerobic abscess of the aortic valve ring can affect contiguous vital structures of the conducting system. Immunosuppression may increase the risk of anaerobic infection after genitourinary procedures, and in this situation the recommended antibiotic prophylaxis may be inadequate.