It is hypothesized that an altered turnover of extracellular matrix mediated by matrix metalloproteinases (MMPs) is present in thoracic aortic aneurysms. Here, we analyzed the occurrence of MMPs and MMP inhibitors in ascending aortic aneurysms in patients with bicuspid and tricuspid aortic valves.Expression of 23 MMPs and their inhibitors was measured in aortic intima/media and adventitia in 109 patients (40 tricuspid, 69 bicuspid, 68 with aortic diameter≥4.5 cm, and 41 with ≤4.0 cm) using Affymetrix Exon arrays (Affymetrix, Santa Clara, Calif). Gene expression was confirmed by quantitative real-time polymerase chain reaction. Principal components analysis was used to study differences in gene expression. Immunohistochemistry was used to study protein expression.We detected messenger RNA expression for gelatinases (MMP2 and MMP9), stromelysin 3 (MMP11), all membrane bound MMPs (MMP14, MMP15, MMP16, MMP17, MMP24, MMP25), MMP19, MMP21, and MMP28 in ascending aorta. No expression of collagenases was detected. Principal components analysis showed that changes in mRNA expression between dilated and nondilated aorta were mainly detected in patients with tricuspid aortic valves. MMP14 and MMP19 showed higher expression in dilated aortas and MMP19 expression correlated positively to maximal aortic diameter in patients with tricuspid aortic valves (Rho=0.61, P=.004, and Rho=0.57, P=.008, using raw and body surface area-corrected aortic diameter, respectively). Immunohistochemical staining demonstrated increased medial expression of MMP14 and MMP19 in dilated aorta.The present study identifies MMP14 and MMP19 as proteolytic enzymes potentially involved in aneurysm formation in the ascending aorta of patients with tricuspid aortic valves.