Little information is available concerning the normal systolic pattern of movement of the interventricular septum in man. Accordingly, 242 patients without clinical or catheterization evidence of right ventricular volume overload (RVVO) were studied employing the ultrasound continuous recording technique. In the plane of the mitral valve, systolic anterior septal motion (SASM) was present in 111 patients; in 38 patients the septum did not move during systole while in 74 patients, septal motion was variably anterior and posterior during the same recording. Normal posterior septal motion occurred in only 19 patients. However, at or below the level of the chordae tendineae, 226 of the 242 patients (93%) had normal posterior septal motion; the other 16 patients had severely impaired left ventricular function. In 56 patients with RVVO, 34 had abnormal septal motion at the level of the chordae tendineae, 24 with SASM, 7 with variable motion and 3 with no movement. To evaluate septal motion further, 100 normal subjects were studied using a phased multicrystal ultrasound system which provided a sagittal plane image of the cardiac structures. In all 100 subjects the superior septum moved anteriorly in systole with the aortic root, and the upper one third of the septum acted as a 'hinge' for the lower two thirds which moved posteriorly. In 8 of 21 patients with RVVO, studied by the multicrystal method, the entire septum moved anteriorly during systole; variable patterns occurred in 7 patients, while normal septal motion was present in 6 patients. It is concluded that normal septal motion consists of anterior movement of the superior segment of the septum during systole; below a pivot point, the inferior two thirds of the septum moves posteriorly during systole; the normal pivot point of the septum frequently results in SASM when recordings are made in the plane of the mitral valve in patients with and without RVVO; and that paradoxical septal motion is not always present in patients with RVVO even when echocardiographic recordings are obtained at or below the level of the chordae tendineae.