To assess whether paradoxical (systolic anterior) motion of the interventricular septum is a true abnormality of septal contraction caused by right ventricular volume overload, we examined the regional pattern of left ventricular contraction in 20 patients with an atrial septal defect within the oval fossa using a fixed and floating reference system of analysis of wall motion. The patients, with a median age of 6.8 (3.5–13.4) years, had a Qp/Qs ratio of 3.5:1 (1.2:1–8:1). They were studied by cross-sectional echocardiography four days (3–5) before and 14.5 (3–67) days after surgical closure of the atrial septal defect. The postoperative Qp/Qs ratio was 1.1:1 (0.9:1–2:1). Regional wall motion of the left ventricle was analyzed in the parasternal short axis view at the level of the mitral valve and papillary muscles as well as in the apical four-chamber view. The endocardium was digitized manually in end-systolic and end-diastolic frames. The center of mass of this figure was calculated and connected to an outside reference point in the right ventricle. With the floating system, both centers of mass and the reference lines were superimposed, thus correcting for movement of the heart inside the thorax. With the fixed system,both end-diastolic and end-systolic frames were measured separately without correcting for movement of the heart. The left ventricle was divided in eight segments in a clockwise fashion and regional change in area was measured and compared to 40 normal age matched controls. With the floating system, left ventricular regional wall motion was normal in all patients before and after closure of the atrial septal defect and, thus, was not influenced by the change in right ventricular volume load. With the fixed system, both before and after surgical closure of the atrial septal defect, left ventricular regional wall motion was reduced in the two segments representing the basilar and middle portion of the interventricular septum. The floating system of analysis of left ventricular regional wall motion has the ability to correct for movement of the heart, which makes the supposed “abnormal” systolic anterior motion in right ventricular volume overload, a condition prevalent in patients with atrial septal defect, disappear. Thus, we conclude that the so-called paradoxical septal motion in atrial defect is an artifact. This may be caused by an increased motion of the heart but is unrelated to the volume load of the right ventricle.