Two-dimensional echocardiography (2DE) and angiography are sensitive and specific when assessing septation defects but provide limited information regarding defect shape and relationships to intracardiac structures, Dynamic 3Dechocardiography (3DE) may provide a unique ability to define and present defect shape and relationship to intracardiac structures. To assess this, we performed 3DE dynamic reconstruction of 25 septation defects in 19 sedated infants and children. Each patient had a computer-driven subxiphoid rotating scan at 10 intervals through 180°. Data were processed into a cubic 3-D data set from which cut planes were defined. A rotating 3DE reconstruction of the intracardiac anatomy sliced at a given plane was displayed. Dynamic 3DE images were compared with: 2-D in all, angiography in 18, and videotaped surgical views in 7. Septal defect identification was as follows: For all septation defects completely defined by 3DE (11 VSD; 7 ASD) defect shape, breadth and spatial relationships were clearly displayed in a single projection. With 2DE and angiography, on the other hand, multiple views were necessary to reconstruct a limited mental idea of septal defect characteristics. Of the 5/16 VSDs and 2/9 ASDs not completely appreciated with 3DE: 5 had suboptimal 3DE due to poor 2-D image quality and motion artifact; 1 was a shallow inlet VSD obscured by AV valve tissue; and 1 was a moderate size posterior secundum ASD partially imaged from a 4-chamber 3DE projection. Septation defect 3DE reconstructions closely resembled surgical images in 717. Conclusion Though less sensitive than 2DE/angiography, subxiphoid rotational 3DE provided: (1) improved understanding of septation defect shape and spatial relationships; and (2) a unique ability to display septation defects using right heart surgical projections.