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Objectives: Certain aortic valve malformations predispose to ascending aortic aneurysm, although the mechanisms are incompletely understood. The aim of this study was to determine whether turbulence across the unicuspid aortic valve (UAV) contributes to regional differences in endothelial nitric oxide (eNOS) signaling in the ascending aortic wall. Methods: Samples were collected intraoperatively from the convex and concave ascending aortic wall from 64 patients with tricuspid aortic valves (TAVs; 25 nondilated, 17 dilated), or UAVs (9 nondilated, 13 dilated). Results: In normal-sized aortas, eNOS protein was decreased in UAV compared with TAV (P = .02) whereas mRNA was similar (P = .62). eNOS protein was increased in UAV-dilated aortas compared with UAV-nondilated aortas (P = .04), whereas dilatation had no impact on eNOS protein levels in TAV aortas (P = .73). Comparing only aneurysmal aortas, we found no difference in eNOS mRNA or protein between dilated TAV and UAV aortas (P = .26, P = .76). For eNOS mRNA and protein levels in normal and dilated UAV-associated aortas, no differences were found between concavity and convexity (all P > .05). This differed from dilated TAV aortas, which showed decreased eNOS mRNA in the convexity (P = .004) whereas eNOS protein levels were similar (P = .75). Conclusions: eNOS downregulation is observed in the UAV-associated ascending aorta and is apparently independent of dilatation. No regional differences were found, however, which would be expected if eNOS changes occur due to wall shear stress. This implies a congenital defect in eNOS signaling that may be stronger than turbulence-induced expression patterns. Further research should define the role of eNOS in aortopathy associated with aortic valve disease.