For infants with valvar aortic stenosis, balloon aortic valvuloplasty has supplanted surgical valvotomy as the initial treatment of choice at most institutions. Technological innovations have resulted in further miniaturization of balloon dilation catheters, allowing this procedure to be performed through smaller sheath sizes. Currently, the Tyshak-Mini balloon dilation catheter (B. Braun Medical) allows passage of up to an 8 mm dilation balloon catheter through a 3 Fr hemostatic sheath. The efficacy of this system for the treatment of valvar aortic stenosis in infants less than 6 months of age was evaluated in 20 patients undergoing 22 procedures. Mean age at the time of intervention was 26 +/- 46 days. Mean transvalvar gradient was 76 +/- 22 mm Hg prior to balloon dilation. Following balloon valvuloplasty, residual gradient was 26 +/- 12 mm Hg, reflecting a mean change in peak-to-peak gradient of 49 +/- 19 mm Hg. Postintervention increase in aortic insufficiency was one grade or less in 19/22 procedures, two grades in 2 procedures, and three grades in 1 procedure. There were no significant vascular complications reported immediately following the procedure. Repeat valvuloplasty was performed in three patients in which the 3 Fr system was used in two patients. The 3 Fr system for balloon aortic valvuloplasty in infants less than 6 months of age is effective and safe.