The majority of pulsatile flow simulators used to assess the hydrodynamic function of artificial heart valves consist of modular rigid chambers and a positive displacement pump with an infinite input impedance. However, this, coupled with the highly compliant nature of tissue roots, results in extreme pressure and flow oscillations. The Leeds pulsatile flow simulator was modified to incorporate additional compliance chambers at the pump/ventricular interface. Bioprosthetic aortic roots and a stented porcine aortic bioprosthesis were tested in this modified simulator, at maximum and minimum compliance. The resulting pressure and flow waveforms at maximum compliance for the fixed aortic roots were comparable with those for the stented bioprosthesis, thus allowing direct comparison of the characteristics of these two different devices. An appropriate physiological model for the hydrodynamic testing of compliant tissue roots has been established.