Numerical simulation of blood flowing through Bileaflet Mechanical Heart valves (BMHV) has been widely performed in the past to achieve the unprecedented details of the cardiac mechanics of BMHV and the associated blood flow field. However, most of the past studies have assumed the blood to be Newtonian fluid. Although in large arteries like aorta, blood behaves as a Newtonian fluid, however its Non-Newtonian effects can become important as it passes through regions with low shear rates. This paper has modelled blood as a non-Newtonian incompressible fluid and complete physiological cardiac cycle has been simulated. Arbitrary Lagrangian Eulerian approach has been employed to establish blood-leaflet interaction. The results indicated a 58 higher average wall shear stress on the fully closed leaflets when modelling blood as non-Newtonian fluid compared to Newtonian modelling. Therefore, the paper concludes that the blood must be modelled as non-Newtonian fluid to achieve accurate hemodynamics. © 2018 Author(s).