Introduction: Bicuspid aortic valve (BAV) is included among developmental abnormalities of the great vessels. Aortic and pulmonary roots share a common embryologic origin, therefore combined histopathologic changes of the media are seen in the ascending aorta and pulmonary artery (PA) in BAV. There is few data on PA stiff ness in these patients (pts). Purpose: To assess the correlates of PA dilation and elastic properties by echocardiography in BAVs with aortic regurgitation (AR). Methods: We enrolled 53 BAV pts (38 ± 12 years, 62% men) with AR. Exclusion criteria: inadequate acoustic window, right ventricle dilation/dysfunction, PA hypertension or disease. Dilated ascending aorta and PA were defi ned by dimensions > 36 mm and > 23 mm, respectively. PA areas and indexes of stiffness were measured: pulsatility (%) = (PAs-PAd)/PAd*100; elastic modulus (mm Hg) = PP*PAd/(PAs-PAd); PA distensibility (%/mm Hg) = [(PAs-PAd)/pp*PAd]*100; capacitance (mm3/mm Hg)=SV/PP; dynamic compliance (mmHg-1) = (PAs-PAd)*10000/PAd*sPAP; elastance (mm Hg/ml) = sPAP/SV, stiff ness index β (SI) = LN(sPAP/dPAP)/[(PAs-PAd)/PAd], where PAs and Pad – systolic and diastolic PA area, respectively, SV – right ventricular stroke volume, PP – pulmonary pulse pressure, sPAP, dPAP – systolic and diastolic PA pressure. Results: Mean end-diastolic ascending aorta and PA diameters were 38 ± 7 mm and 22 ± 3 mm, respectively. In the study group, 57% pts had dilated ascending aorta and 38% PA dilation. At univariate analysis, PA diameter correlated with PA capacitance (r =.60, p < .001), pulsatility (r = -.33, p = .017), dynamic compliance (r = -.34, p = .014), distensibility (r = -.34, p = .015), elastic modulus (r = .44, p = .001) and SI (r = -.281, p = .017). Pts with dilated PA trunk had higher ascending aorta diameter (p = .004) and PA length (p = .007) and impaired PA elastance (p = .001), capacitance (p < .001), pulsatility (p = .017), dynamic compliance (p = .018), distensibility (p = .02) and elastic modulus (p = .006). The PA stiffness parameters did not correlate with PA pressures. Conclusions: In BAV pts with aortic regurgitation, PA diameter correlated with the elastic properties of PA. Moreover, PA dilation signifi cantly correlated with ascending aorta dilation and PA stiff ness parameters irrespective of PA pressures. Further prospective studies are needed to assess the prognostic signifi cance of these fi ndings.