The noninvasive detection of an aneurysm of the interventricular septum may be predictive of spontaneous closure of a ventricular septal defect. Moreover, in patients with audible systolic clicks the distinction must be made between septal aneurysm and mitral valve prolapse. The current report describes the echocardiographic visualization and pattern of motion of an aneurysm of the membranous ventricular septum. The diagnosis was made by both single crystal and real-time cross-sectional, multiple crystal ultrasound techniques prior to catheterization. These findings from the basis of the present study.