The implantation of Mechanical Heart Valves has been linked to thrombus formation within the cardiovascular system, with flow-induced platelet activation suggested as one of the major mechanisms leading to this pathology. Platelet activation may lead to formation of thromboemboli in the blood stream, posing a significant risk to the patient by having the potential to obstruct blood flow in small blood vessels, e.g., in the brain, thereby increasing the likelihood of cardioembolic stroke. While many hemodynamic mechanisms contribute to this phenomenon, the primary factors are regions of elevated flow stress and recirculation zones. The aim of this investigation is to characterize blood flow across a 27 mm monoleaflet Medtronic heart valve via numerical simulations using Computational Flow Dynamics (CFD). CFD is used in a 2D geometry to solve both steady flow and transient flow. The numerical results are compared to an experimental study in which a non-invasive flow measurement technique, Digital Particle Image Velocimetry (DPIV), is used to map the velocity vectors in the area downstream the valve. DPIV employs a Nd:YAG Laser to highlight latex particles as they pass through the valve. A CCD camera is used to record the flow fields, while software analyzes the images, using spatial cross-correlation technique, to compute the velocity fields. Dynamic Similarity, necessary to substantiate any correlations between the experimental setup and the numerical simulations, is achieved by maintaining the same Reynolds Number. Preliminary results indicate regions of increased velocity surrounding the leaflet in addition to a decrease in velocity along the vessel walls. Shed vortices and a distinct recirculation zone has been mapped immediately downstream the valve. Normal flow was restored further downstream. The DPIV measurements had validated the predictions of the CFD simulations. These flow conditions are conducive to platelet activation and aggregation, increasing the risk of thromboembolism.