In this paper, the influence of the upstream boundary condition for the numerical simulation of an aortic Bileaflet Mechanical Heart Valve (BMHV) is studied. Two types of upstream boundary conditions are discussed and evaluated. First, an inflow velocity profile is imposed at the inlet of the valve. Secondly, a geometrical boundary condition is used, which implies that the flow rate is governed by the geometrical contraction of the left-ventricle (LV). Both boundary conditions are used to simulate a 3D case with the same BMHV. The change in time of the LV volume is calculated such that the flow rate through the valve is identical in both cases. The dynamics of the BMHV are modelled using fluid-structure interaction (FSI) and only the opening phase of the valve is simulated. The simulations show that although the results for the two cases are similar, differences occur in the leaflet movement. In particular, when using the velocity profile, the leaflets impact the blocking mechanism at their open position with a 25% larger angular velocity. Therefore, when one wants to simulate the dynamics of such an impact, the upstream boundary condition needs to be chosen carefully.