Pulmonary balloon valvuloplasty (PBV) is an effective method to treat congenital valvular pulmonic stenosis, but the ideal balloon-anulus ratio (BAR) for this procedure remains unclear. We studied 71 procedures where BARs of 1.0-1.5 were used, since it has been shown that a ratio of < 1.0 is less effective and that of > 1.5 may produce more complications. A curvilinear relation was found between BAR and the fractional fall in haemodynamic parameters reflecting stenosis severity, both immediately after dilatation and at follow-up. Best results were observed with a BAR of 1.25, with progressive worsening on either side of this ratio. The relationship remained significant in multiple regression analysis involving age, sex and baseline haemodynamic variables. The data show that a BAR of 1.25 is probably the ideal ratio for PBV.