Echocardiography was used to evaluate interventricular septal motion in 17 patients with congenital cardiac defects that produced either left-to-right shunts at the atrial or tricuspid insufficiency. Fourteen patients had abnormal septal motion: 12 had type A and 2 had type B motion. Two previously unreported causes for abnormal interventricular septal motion (total anomalous pulmonary venous return and partial anomalous pulmonary venous return) were found to produce echocardiographic findings identical to those found in patients with atrial septal defect. Three patients with significant left-to-right shunt at atrial level had normal septal motion. When abnormal septal motion is present, it is suggestive of right ventricular overload. However, such motion is not specific enough to differentiate among the defects that produce right ventricular volume overload or to distinguish a patient with an abnormal volume overload from one with normal volume.