An analysis of the dynamics of a mechanical monoleaflet heart valve prosthesis in the closing phase is presented. The backflow velocity of the fluid and the pressure distribution on the occluder during the closing phase were computed using a control volume approach in the unsteady state. Using moment equilibrium principles on the occluder motion and the squeeze film dynamics of the fluid between the occluder and the guiding strut at the instant of impact, the velocity of the occluder tip and the impact force between the occluder and the guiding struts were computed. The dynamics of fluid being squeezed between the occluder and the guiding struts are accounted for by Reynolds' equation. The effect of the fluid being squeezed between the occluder and the guiding strut was to reduce the velocity of the occluder tip at the instant of valve closure as well as to dampen the fluttering of the occluder before coming to rest in the fully closed position. The squeeze film fluid pressure changed rapidly from a high positive value (10 MPa) to a relatively large negative value (-15 MPa) in < 1 msec. The results of this study may be extended for the analysis of cavitation inception and mechanical stresses on the formed elements and valve components, as well as to estimate the endurance limits of prosthetic valves.