Introduction. Real-time 3-dimensional echocardiography (RT3D echo) is a novel technique capable of instantaneous acquisition of volumetric data. We propose a new approach to derive a complete dynamic anatomical model of the left atrium during atrial fibrillation (AF) episodes by using both RT3D transthoracic echocardiogram (RT3D-TTE) and RT3D transesophageal echocardiogram (RT3D-TEE). Methods. 3D patient-specific anatomical and motion models were derived from RT3D-TTE and RT3D-TEE. By applying a deformable region-based approach, we extracted the LA and the LA appendage models from RT3D-TTE and RT3D-TEE, respectively. A two-step registration was then applied: an iterative closest point algorithm was first applied to fuse RT3D-TEE and RT3D-TTE in the same domain; then, an affine transform followed by a B-spline registration was used to obtain the motion model in AF throughout the cardiac cycle. This approach was tested on 5 consecutive AF patients. Results. The proposed workflow was successfully applied to all patients. Val-idation of the derived motion model was only qualitatively performed not being available a reference motion field during AF. However, the computed displacement of the LA model throughout the cardiac cycle was representa-tive of the small amplitude of wall contraction in AF (mean displacement throughout the cardiac cycle +/- SD (mm): 1.5+/-0.7, displacement range (mm) [0.1- 2.7]). Conclusions. We presented a unique approach to derive a dynamic anatom-ical model of the LA during AF episodes. Preliminary results are promising but further testing on a larger population is required.