BACKGROUND: Plaques in blood vessels exhibit a wide range of stiffness depending on disease conditions: stiffness is an important factor in plaque behavior. The geometrical change in plaque based on its behavior can affect blood flow patterns. Thus, it is important to study both blood flow and deformation of plaques and blood vessels. OBJECTIVE: This study aims to identify the differences in flow conditions between in vitro models to discuss experimental materials for arterial wall and flow observation. METHODS: In order to observe the blood flow pattern and plaque deformation simultaneously, a PVA-H stenosis model was used. In addition, a silicone model was also used as a rigid-like model for comparison with the PVA-H model. PIV was employed to measure the flow velocity distribution and determine the flow levels in the models. RESULTS: PVA-H model exhibits expansion with an increase in upstream pressure and silicone model maintains the diameter. The expansion depends on their mechanical properties and influences flow conditions such as velocity changes and RAP in the parent artery. The balance between the expansion and change in flow conditions determines the final geometries of PVA-H model and flow pattern. CONCLUSIONS: The results suggest that the stiffness measurement for blood vessels and plaques such as ultrasound measurements would be important for accurate treatments.