Four mechanical bi-leaflet prostheses, the St. Jude Medical (SJM) valve and On-X (OX) valve with straight leaflets and the Jyros (JR) valve, and Edwards MIRA (MIRA) valve with curved leaflets were tested in the mitral position under pulsatile-flow conditions. Dynamic PIV system was employed to analyse the flow field affected by the leaflet shapes and overall valve designs. Detailed analysis of the time resolved information of the flow fields associated with the changing flow phases revealed the significance of the leaflet shape and overall valve designs on the flow field.