Aim of this study is to determine the left and right ventricle functions by echocardiography in patients with newly diagnosed obstructive sleep apnea (OSA) and to investigate whether there is a relationship between the apelin levels and systolic and diastolic functions of the right and left ventricles. Study included 44 patients (30 males, 14 females; mean age 49.8±11.5 years) diagnosed with obstructive sleep apnea according to polysomnographically determined apnea hypopnea index, and 30 control subjects (25 males, 5 females; mean age 43.03±10.89 years) diagnosed with simple snoring. Apelin levels of all the study subjects are measured. Systolic and diastolic functions of both ventricles were evaluated with the help of conventional and tissue Doppler methods. Results: Systolic and diastolic blood pressure levels of the OSA group were significantly higher compared to those of the AHI control group. Lateral inferior and anterior E’ were significantly lower whereas E/E’ was significantly higher in the OSA group compared to the control group (8.40±3.24 vs. 10.80±3.24; p=0.001, 7.50±2.60 vs 9.00±2.51; p=0.009, 7.90±2.68 vs. 8.90±2.73; p=0.006, 7.57±3.20 vs. 6.44±1.55; p=0.023, respectively). Although the apelin levels were higher in the OSA group compared to the control group, this difference did not reach statistical significance. Age, AHI, and echocardiographic indices were not correlated with the apelin levels. There was no relationship between the severity of OSA and the apelin levels, either. This study showed diastolic functions may be impaired in patinets with newly diagnosed OSA. Apelin levels which has been shown to play an important role in cardiovascular hemodynamics, had no significant correlation with OSA severity. Moreover, there was no significant correlation between the apelin levels and echocardiographically assessed systolic and diastolic functions of both ventricles.