A postmortem investigation was carried out of 19 heart specimens with transposition of the great arteries, ventricular septal defect, and congenital subvalvular pulmonary stenosis. Certain types of obstruction appeared to be closely related to other features of the hearts. In cases with malalignment of the infundibular septum, the obstruction was caused by this septum and the anterolateral muscle bundle of the left ventricle. If the infundibular septum was deviated considerably to the left, the pulmonary stenosis was usually severe because the infundibular septum and anterolateral muscle bundle were joined. This junction resulted in a relatively posterior position of the pulmonary orifice in the left ventricle. A less extreme deviation of the infundibular septum resulted in an obstruction by this septum and by the anterolateral muscle bundle, situated at the right and the left sides of the pulmonary orifice respectively. In some cases of paratricuspid ventricular septal defect an anomalously attached and cleft anterior leaflet of the mitral valve was found. This, together with a leftward deviation of the anterior left ventricular part of the ventricular septum, caused the obstruction.