A total of 31 specimens of hearts with congenital pulmonary valvar stenosis were studied. To define the anatomy of the normal pulmonary valve, 210 specimens of hearts considered to have a normal pulmonary valve were also reviewed. On the basis of gross morphology of the valve leaflets and annulus, the stenotic valves were subgrouped into domed, unicommissural, bicuspid, tricuspid, hypoplastic annulus, and dysplastic. The valve leaflets in all subgroups were thickened. The thickness varied in degree, but involved the entire length of the leaflet. Microscopically, the thickness in most cases was due to an increase in myxomatous tissue. In a few cases, the elastic and collagen components of the leaflet were increased. The valve annulus was abnormal in most cases. The abnormalities included replacement of the fibrous backbone of the annulus by myxomatous tissue and partial or complete absence of the annulus. The impact on valvar anatomy by direct surgical valvotomy (14 patients) and closed Brock valvotomy (two patients) was reviewed. Precise knowledge of pulmonary valve anatomy is an aid to successful balloon pulmonary valvuloplasty.