From January 1981 to December 1990, intracardiac repair of tetralogy of Fallot in 148 pediatric patients, with one surgical death, was directed toward preservation of the native pulmonary valve. Using the accepted preoperative angiographic criterion for the pulmonary valve annulus area (PVA) of 1.8 cm2/m2, 85 patients were candidates for transannular right ventricular outflow patch (TAP). However, in 54 patients with a mean PVA of 1.5 cm2/m2 (range 1.06-1.76), the valve was preserved without using TAP because the morphological changes (cusp thickening and annular distensibility) seemed acceptable for preservation in view of its probable hemodynamic efficiency and growth potential. A morphological classification of pulmonary valve changes has evolved. Retrospectively, 24 (77%) of the 31 patients with TAP had moderate to severe cusp thickening and ring rigidity; this incidence was significantly higher (p < 0.001) than that in preserved patients (18 of 54 or 33%). The incidence of morphological changes increased with operative age; that is, 2 of 13 (15%) patients younger than 1 year versus 23 of 40 (58%) patients older than 4 years (p < 0.01). All 54 patients with preserved pulmonary valves were catheterized one month postoperatively. The intraoperative right to left ventricular systolic pressure ratio (RVP/LVP) decreased significantly (p < 0.005) in one month, from a mean of 0.79 (range 0.44-1.36) to 0.57 (range 0.36-0.97). The PVA increased from a mean of 1.5 to 1.9 cm2/m2 (range 1.20-2.65), and the rate of its increase was significantly larger (p < 0.005) as operative age decreased. Pulmonary valve regurgitation of greater than mild degree occurred in 8 of 54 (15%) patients with the valve preserved.(ABSTRACT TRUNCATED AT 250 WORDS)