Byline: Atefe Rajaei; Kamran Hassani; Ali Tavakoli Golpaygani Abstract In this study, mitral regurgitation was investigated using fluid-structure interaction method in 3 dimensions. The fluid-structure interaction modeling technique has been widely used for a wide range of applications in bioengineering sciences. However, despite all these advances, such studies in the field of cardiovascular complications are still limited, and the need for further research and studies seems necessary. Using these methods, the results can be obtained without the need for complex laboratory devices and systems and without spending a lot of time and money and only by modeling the behavior of the mitral valve. In this study, we tried to simulate the hydrodynamics of blood flow and its interaction with the return flow through the mitral valve using numerical solution software and validate it with the available laboratory results. A 3-dimensional numerical simulation was performed for the complete closure of the mitral valve leading to a return flow. Mitral valve, left atrium, and left ventricle were made. These images, consisting of 240 slices, were taken by a multislice computed tomography scan machine, converted to volume in supersonic Geomagic software, and then entered in ANSYS software. Fluid-structure interaction analysis was performed on the project, and the results were reported. Evaluation and comparison of the results show that von Mises stress and shear stress on the valve wall are higher in the normal state than all other conditions, whereas the velocity and pressure of blood flow in the normal state are less than other states. The highest shear stress, von Mises stress, blood flow velocity, and pressure, as well as the greater distance between the 2 leaflets, are the main parameters that affect the abnormities of mitral valve function.