Abstract - The clinical meaning of left atrial vortex has been not fully elucidated. We developed a new left atrial model to simulate intra-atrial flow and a simple method to observe atrial vortex by magnetic resonance imaging (MRI). A flow simulation model of the left atrium (LA) was developed based on slices of the LA image acquired by 1.5T MRI scanner system. Images were reconstructed by commercial software and a computational model was created by using tetrahedral mesh. In order to give the model consecutive temporal change, we presumed that deformation of LA is related to mitral valve annular movement. Then we traced its temporal change and approximated. The flow simulation was performed with FLUENT. Pressure boundary conditions were set based on data in a literature. The results of flow simulation in LA were validated qualitatively by MRI velocity mapping. Left atrial vortex was observed in both simulation and MRI velocity mapping. A representative slice to observe left atrial vortex by MRI was determined with the assistance of the simulation model.