Background/aim: We investigated whether obstructive sleep apnea syndrome (OSAS) has any impact on pulmonary artery distensibility (PAD) and right ventricular (RV) function. Materials and methods: Subjects were categorized according to apnea?hypopnea index (AHI) as follows: controls (n = 17 and AHI < 5), mild-to-moderate OSAS (n = 22 and AHI = 5?30), and severe OSAS (n = 29 and AHI > 30). All subjects underwent transthoracic echocardiography a er polysomnography to assess PAD and RV function. PAD was recorded as M-Mode trace of the right pulmonary artery and was de ned as (PAmax ?PAmin/PAmin) × 100. S? was measured by means of TDI of the lateral annulus of the RV using apical four-chamber view. Results: Patients with severe OSAS demonstrated impaired RV longitudinal systolic function (S?) compared to the other groups (P < 0.05). Impaired pulmonary vasculature elastic properties as re ected by decreased PAD were more prevalent in severe OSAS (26.2 < 5.7%) compared to the controls (29.9 &pm; 4.6%; P < 0.05) and mild-to-moderate OSAS (29.0 &pm; 4.1%; P < 0.05). An inverse relation between PAD (P < 0.05), RV myocardial performance index (MPI) (P < 0.05), and AHI was demonstrated. S? also correlated with PAD (P < 0.05). Conclusion: PAD is a signi cant tool to evaluate pulmonary vasculature sti ening and is well correlated with disease severity in OSAS. Further, impaired PAD may lead to RV systolic dysfunction.