AIMS: A novel real-time three-dimensional echocardiography (RT3DE) analysis tool specifically designed for evaluation of the left atrium enables comprehensive evaluation of left atrial (LA) size, global, and regional function using a dynamic 16-segment model. The aim of this study was the initial validation of this method using computed tomography (CT) as the method of reference. METHODS AND RESULTS: The study population consisted of 34 prospectively enrolled patients with clinical indication for pulmonary vein isolation. A dynamic polyhedron model of the left atrium was generated using RT3DE. LA maximum and minimum volumes (LA(max)/LA(min)) and emptying fraction (LAEF) were determined and compared with the results obtained by CT. High correlations between RT3DE and CT were found for LA(max) (r = 0.92, P > 0.001), LA(min) (r = 0.95, P > 0.001), and LAEF (r = 0.82, P > 0.001). LA(max) and LA(min) were lower by RT3DE than by CT (95.0 +/- 44.7 vs. 119.8 +/- 50.5 mL, P > 0.001 and 58.1 +/- 41.3 vs. 83.3 +/- 52.6 mL, P > 0.001, respectively), whereas LAEF was measured higher by RT3DE (42.8 +/- 15.2 vs. 34.2 +/- 15.4%, P > 0.001, respectively). RT3DE measurements closely correlated in terms of intra-observer (intra-class correlation r = 0.99, r = 0.99, r = 0.96, respectively) and inter-observer variability (r = 0.97, r = 0.98, r = 0.88, respectively). CONCLUSIONS: LA volumes and EF as assessed by RT3DE correlate highly with CT measurements, albeit there is some bias between the imaging modalities. Most importantly, RT3DE measurements using the novel dedicated LA analysis tool are robust in terms of observer variability and thus suitable for follow-up analyses