BACKGROUND AND AIM OF THE STUDY The durability of freehand-sewn aortic valve homografts used for valve replacement in humans is greater than for stented aortic homografts. In analogy with this, it is expected that the durability of a stentless heterograft will be superior to that of its stented counterpart. Our objective was to investigate the influence of stenting on amino-oleic acid (AOA)-treated, glutaraldehyde-fixed porcine aortic valve bioprostheses. METHODS Twelve young sheep underwent implantation of porcine aortic valves in the pulmonary artery: six porcine aortic stentless valves (Freestyle) and six porcine aortic stented valves (Mosaic). In each series, three valves were explanted after three months, and three after six months. Valves were analyzed by gross inspection, radiography, histology, and transmission electron microscopy. Quantitative determination of calcium content was made with atomic absorption spectrometry. RESULTS The porcine aortic stentless valve showed extensive calcification of its aortic wall portion, but had perfectly functioning, pliable cusps without calcification up to six months. The cusps of porcine aortic stented valves were also pliable and functioning without calcification up to six months. Only minimal calcification was seen in the aortic wall of the stented valves. At six months after implantation the cusps of stentless valves contained significantly less calcium than those of stented valves (2.7+/-1.2 microg/mg and 7.9+/-2.3 microg/mg, respectively; p = 0.011). However, the aortic wall from stentless valves contained significantly more calcium than that of stented valves (three-month explants: 39.2+/-14.4 versus 7.2+/-2.8 microg/mg; p <0.05; six-month explants: 49.3+/-14.0 versus 14.1+/-5.9 microg/mg; p <0.05). CONCLUSION These data suggest that stenting does influence cuspal calcification of AOA-treated, glutaraldehyde-fixed porcine aortic valves.