Vascular prostheses currently used in aortic replacement surgery do not have the same mechanical properties as human arteries. In vivo studies have revealed that aortic grafts augment heart load and alter blood pressure and flow waveforms. A one-dimensional model of the arterial tree was developed in order to analyze the different mechanisms by which grafts placed in the ascending aorta (proximal) and descending aorta (distal) affect hemodynamics. Graft compliance and properties were based on in vitro tests. Predicted pressures at the aortic root were compared for the control, proximal and distal graft case. Pulse pressure increased by 21% and 10% in presence of a proximal and distal graft, respectively. The distal graft resulted in a wave reflection coefficient of 0.60 whereas for the proximal graft the wave reflection coefficient was 0.46. The physiological mechanism behind the rise of pressure is dual and it is critically affected by the graft's compliance and position. In case of a proximal graft, the primary reason for aortic pressure increase is the augmentation of aortic characteristic impedance, which augments the forward pressure wave, whereas for the distal graft the wave reflections are major contributors to the total pressure wave. Overall, the proximal graft altered hemodynamics to a greater extent than a distal aortic graft. © 2011 IEEE.