With cardiovascular diseases (CVD) being the leading cause of death worldwide, computational fluid dynamics can be used to provide insight into the onset and progression of CVD and to improve the design of medical devices. This thesis develops novel cardiovascular simulations to evaluate how the multiphase rheology of blood impacts CVD and the activation of platelets, with an assessment of haemodialysis catheter design. To date all cardiovascular models assume a smooth artery wall, despite microscopic surface roughness being linked to CVD. A simulation of artery roughness showed a greater range in haemodynamic parameters associated with CVD, compared to a smooth wall, with increased residence time in an ultra low-shear environment (