Mechanical and conventional stented bioprostheses, because of need for anticoagulants, hemodynamic characteristics and long-term durability, do not represent the optimal heart valve replacement device. In this study we compared the hemodynamic function of a stented aortic bioprosthesis (St Jude Bioimplant), implanted in 10 patients, with a stentless porcine aortic bioprosthesis (Biocor) implanted in 7 patients, by means of Doppler echocardiography early postoperative at rest (T1) and 6 months later at rest (T2a) and during exercise (T2b). Mean and peak systolic gradients across stentless porcine prostheses were significantly lower than across stented bioprostheses (T1 p = 0.008 and p = 0.004; T2a p < 0.0001 and p < 0.0001; T2b p < 0.0001 and p < 0.0001, respectively). Our results show that systolic and diastolic mechanical stress on biological components of a glutaraldehyde-fixed stentless porcine aortic bioprosthesis is much lesser than on stented bioprostheses. This feature has appeared evident at rest and much more after exercise testing. The reduction of systolic and diastolic stress is expected to determine lower calcification degree and longer durability of stentless porcine aortic bioprostheses. Moreover, aortic valve replacement by means of stentless bioprostheses allows the implantation of a 1 size (2 mm) larger device, appearing favourable especially in small aortic annulus. On the basis of these promising results we suggest that stentless bioprostheses are a valid alternative to stented bioprostheses for aortic valve replacement. However, patient population is too small and the follow-up is too short to draw a definite statement about long-term hemodynamic performance of this device.