This thesis focuses on the hemodynamics assessment in the left atrium through computational fluid dynamics (CFD) simulations, comparing pre- and post-intervention results of the left atrial appendage (LAAO) in two patients affected by non-valvular atrial fibrillation. Six post-LAAO configurations were examined considering various values of atrial wall stiffness and types of catheter models, to assess how changes in these features affects the hemodynamics in terms of residual thrombotic risk. Comparison of pre- and post-operative models demonstrated the influence of modeling approach and elucidated on the importance of optimal device positioning in the post-LAAO hemodynamics. The numerical workflow presented in this thesis proposes a valid tool for the evaluation of the best device implantation to reduce post-interventional complications and thrombotic risk.