Background: Matrix metalloproteinases (MMP) and cathepsins are proteolytic enzymes that are upregulated in diseased aortic valve cusps. The objective of this study was to investigate if elevated cyclic stretch causes increased expression and activity of these proteolytic enzymes in the valve cusp. Methods: Circumferentially-oriented fresh porcine aortic valve cusp sections were stretched to 10% (physiologic), 15% (pathologic) and 20% (hyperpathologic) in a tensile stretch bioreactor for 24 and 48 hours. Expression and activity of MMP-1, MMP-2, MMP-9, TIMP-1, cathepsin L, S, and K were quantified and compared to fresh controls. Cell proliferation and apoptosis were also analyzed. Results: At 10% physiologic stretch, expression and activity of remodeling enzymes was comparable to fresh controls. At 15% stretch, expression of MMP-1, -2, -9, cathepsin S and K were upregulated, while expression of cathepsin L was downregulated compared to controls. A similar trend was observed at 20% stretch, but the magnitudes of up-regulation and down-regulation of expression was less than that observed at 15%. In addition, there was significantly higher cell proliferation and apoptosis at 20% stretch compared to other treatment groups. Conclusions: Elevated mechanical stretch on aortic valve cusps may detrimentally alter proteolytic enzyme expression and activity in valve cells. This may trigger a cascade of events leading to accelerated valve degeneration and disease progression.