The left atrium (LA) is an important chamber of the heart, where the left atrial appendage (LAA) is situated. The LAA is a finger-like extension that develops in the third week of gestation: it is the most prevalent region for thrombosis in atrial fibrillation (AF). It has been investigated how the backflow into the LA affects the filling of the LA. It is the scientific goal of this project to analyze and characterize the flow structures and stresses in the bulk of the flow and at the atrial wall as well as the atrial motion and deformation during the atrium filling phase in the two cases.