Patients undergoing aortic valve repair or replacement with associated alterations in stiffness characteristics often develop abnormalities in the aortic sinus vortex, which may impact aortic valve function. The correlation between altered aortic sinus vortex and aortic valve function remains poorly understood due to the complex fluid dynamics in the aortic valve and the challenges in simulating these conditions. The opening and closure mechanism of the aortic valve is studied using fluid–structure interaction (FSI) simulations, incorporating an idealized aortic valve model. The FSI approach models both the interaction between the fluid flow and the valve’s leaflets and the dynamic response of the leaflets during pulsatile flow conditions. Differences in the hemodynamic and vortex dynamic behaviors of aortic valve leaflets with varying stiffness are analyzed. The results reveal that, during the systolic phase, the formation of the sinus vortex is closely coupled with the jet emanating from the aortic valve and the fluttering motion of the leaflets. As leaflet stiffness increases, the peak vorticity of the sinus vortex increases, and the phase space of the vortex core develops a pronounced spiral trajectory. During the diffusion phase, the vortex strength decays exponentially, and the diffusion time is longer for stiffer leaflets, indicating a longer residence time of the sinus vortex that reduces the pressure difference on the leaflet during valve closure. Changes in leaflet stiffness play a critical role in the formation and development of sinus vortices. Furthermore, the dynamic characteristics of vortices directly affect the pressure balance on both sides of the valve leaflets. This pressure difference not only determines the opening and closing processes of the valve but also significantly influences the stability and efficiency of these actions.