In vitro flow studies in saccular aneurysm models had been investigated using Particle Image Velocimetry over a range of Reynolds numbers (400 to 1, 400) and Womersly numbers (22 to 65). Both steady and pulsating flow experiments had been conducted. It was found that at steady flow condition, a recirculating vortex would be fanned inside the aneurysm. The vortex would become stronger at higher Reynolds numbers but weaker at larger anenrysm size. Under the pulsating flow conditions, the vortex appeared and disappeared at different phase of a cycle. The sequence is only punctuated by quasi-inviscid flow behavior. In vitro flow studies in saccular aneurysm models had been subjected using Particle Image Velocimetry over a range of Reynolds numbers (400 to 1, 400) and Womersly numbers (22 to 65). Both steady and pulsating flow experiments had been conducted. It was found That at steady flow condition, a recirculating vortex would be fanned inside the aneurysm. The vortex would become stronger at higher Reynolds numbers but weaker at larger anenrysm size. Under the pulsating flow conditions, the vortex appeared and disappeared at different phase of a cycle. The sequence is only punctuated by quasi-inviscid flow behavior.