Prolonged therapy is necessary because of the high bacterial densities within vegetations and the relatively slow bacteri- cidal activity of some antibiotics such as -lactams and van- comycin. When the bactericidal activity is known to be more rapid or the likely vegetation bacterial burden is lower, then the clinician may prescribe a shorter duration of antimicro- bial therapy in unique instances. Combination therapy with penicillin or ceftriaxone and an aminoglycoside for 2 weeks is highly effective in viridans group streptococci (VGS) IE90 in very select patients with uncomplicated infection. 