Objectives: We investigated right ventricular (RV) structural and functional cardiac alterations in obstructive sleep apnea (OSA) independent of systemic hypertension and their correlation to the severity of OSA. Methods: Forty-one moderate-to-severe OSA but otherwise healthy patients and 30 body mass index-matched control subjects were included. All subjects underwent 24-hour ambulatory blood pressure monitoring, standard and tissue Doppler imaging of the RV. Results: The OSA group had increased RV wall thickness, impaired right ventricular outflow tract fractional shortening (RVOT fs), tricuspid annular plane systolic excursion (TAPSE), RV myocardial performance index (MPI) and RV myocardial acceleration during isovolumic contraction (IVA) (p < 0.001). Apnea hypopnea index (AHI) and mean pulmonary artery (PA) pressure were correlated with all these indices (p < 0.01 for all). RV free wall thickness (p < 0.001) and IVA (p = 0.006) remained significant predictors of AHI after adjusting for age, body mass index, mean PA pressure, RVOT fs, TAPSE and MPI in a multiple stepwise linear regression model. Conclusions: OSA is associated with impaired RV function despite normal systemic blood pressures. The level of RV dysfunction has a direct relationship with the severity of OSA. RV free wall thickness and IVA are independent predictors of AHI in uncomplicated OSA patients.