Since the development of cardiac bioprostheses, numerous chemical treatments have been assayed to prevent mineralization. The effectiveness of chemical treatments that eliminate lipids from the tissue was tested by combining two models. First, handmade bovine pericardial bioprostheses, subjected to chemical treatment with chloroform/ methanol and glutaraldehyde or treated with glutaraldehyde alone for use as controls, were subjected to mechanical stress in a heart valve, accelerated wear tester (100 x lo6 consecutive cycles). Then, the bioprostheses were unstitched and tissue samples were taken from the portion subjected to maximal stress (Pl) and from that surrounding the sewing ring, which had not been subjected to mechanical stress (P2), for subcutaneous implantation. After 21 and 60 days of implantation, we observed calcification of t e samples subjected to mechanical stress, even after deli i- dating treatment, with no significant differences with respect to the control group. However, the treated samples from the portion not subjected to mechanical stress presented a slighter accumulation of calcium after 60-day implantation (5.60 2 3.09 mg Ca2+/g dry weight of tissue) versus the control group (47.17 * 20.4 mg Ca2+/g dry weight of tissue), the difference of which was statistically significant (p < 0.01). At the time of these medium-term studies, marked calcification was observed in tissue subjected to delipidating treatment in the zones that underwent mechanical stress.