Native heart valve leaflets have anisotropic fibrous microstructure and hence anisotropic mechanical properties. It can be then postulated that a prosthesis showing structural anisotropy can mimic the performance of the native tissue better than an isotropic one. Here we propose block copolymer composites with cylindrical microstructure such as poly(styrene-ethylene/propylene-styrene) (SEPS) as a candidate material for heart valve substitute. Microstructure of such material can be effectively oriented by injection moulding and the anisotropy tuned by changing processing conditions and post processing annealing. In this study we investigate a development of orientation within a simple geometry of centrally injected thin discs moulded from SEPS at various injection rates and temperatures. The microstructure has been mapped using a synchrotron Small Angle X-ray Scattering. Cross-sectional SAXS scans along the thickness of the discs have also been acquired with only 25 micrometers spatial resolution. All samples exhibited highly oriented composite morphology, featuring two outer layers with cylinders aligned in the flow direction, and a core layer in which cylinders were aligned transverse to the flow direction. SAXS measurements allowed evaluation of the extent of the outer and the central layers within the samples as a function of injection moulding conditions. A numerical tool to predict the flow–induced orientation has been developed using rate-of-strain and rotation data generated in Polyflow. It was found that Reduced Strain Model of Wang et al. [1] was able to provide a reasonably good match to experimental data for injection moulded SEPS. The numerical tool can be then used to predict orientation development in complex 3D geometries, like heart valve prostheses, during injection moulding of SEPS and similar materials. [1] J. Wang, J.F. O’gara, C.L. Tucker, J. Rheol. 2008, 52, 1179-1200