[show abstract][hide abstract] ABSTRACT: The purpose of this study was to test the hypothesis that the presence of a subaortic ridge associated with a ventricular septal defect (VSD) is related to a malaligned ventricular septum caused by anterior or posterior deviation of the infundibular septum with or without obstructive lesions of the aortic arch. Thirty-two of 295 patients in whom a diagnosis of VSD was made by two-dimensional echocardiography and who were studied from June 1983 to April 1985 presented with a subaortic shelf. Every patient (p less than .00001) had a malalignment type of defect; the defect was produced by anterior deviation of the outlet septum (without compromise of the right ventricular outflow tract) in 28 and by posterior deviation of the infundibular septum in four. The prevalence of a subaortic shelf in the malalignment VSD group was 82% (32/39). Among the 28 patients with a subaortic ridge and anterior deviation of the outlet septum only three had aortic coarctation, but all four patients with subaortic stenosis and posterior infundibular malalignment had obstructive lesions of the aortic arch--coarctation in three and interruption of the aortic arch in one (p less than .001). We conclude that a malalignment type of VSD may be a consistent feature in patients with VSD and associated discrete subaortic stenosis. We also noted a high prevalence of subaortic ridge in the presence of a malalignment VSD and therefore speculate that there may be a common morphogenesis for malalignment VSD, subaortic shelf, and obstructive lesions of the aortic arch.