Fifty-five consecutive patients with the tetralogy of Fallot underwent intracardiac repair in a 12 month period. A standardized protocol for outflow tract enlargement was used. When the measured diameter of the pulmonary valve ring was at least the "minimum acceptable pulmonary valve ring diameter," primary patch-graft enlargement across the valve ring was not done (Group I, 34 patients); when it was less, primary patch-graft enlargement was done (Group II, 21 patients). The right ventricular-left ventricular systolic pressure ratio (PRV/LV) after repair without patch-graft enlargement across the ring was related to the size of the ring. Sixteen (94 percent) of 17 such patients with normal-sized or large pulmonary valve rings (according to the criteria of Rowlatt, Rimoldi, and Lev) had PRV/LV equal to or less than 0.65; four (80 percent) of five patients with smaller rings but within the 50 percent confidence limits had PRV/LV equal to or less than 0.65; five (56 percent) of nine with still smaller rings but within the 72.5 percent confidence limits had PRV/LV equal to or less than 0.65. In Group II, 15 patients had abnormally small rings, but after patch-graft enlargement the mean PRV/LV was 0.44 +/- 0.140. A surgical protocol based on these data has been developed.