In this study, our aim was to evaluate the LV (left ventricle) subclinical myocardial dysfunction using the two-dimensional speckle tracking echocardiography (2D-STE) method on obstructive sleep apnea (OSA) patients with preserved left ventricular ejection fraction (LVEF) and without any confounding disease that may result myocardial dysfunction. Twenty-one healthy individuals and 58 OSA patients were enrolled in the study. The patients were categorized into mild, moderate and severe OSA groups according to the apnea-hypopnea index (AHI). Conventional- and tissue Doppler echocardiography imagings were performed in all the individuals besides the 2D-STE. The longitudinal strain (S) and systolic strain rate (SR(S)) values decreased as the severity of disease increased from moderate towards severe OSA. The circumferential S and SR(S) values were observed to be lower in the severe OSA patients. Despite the increase in the radial S and SR(S) in moderate and mild OSA patients, these measurements decreased in those with severe OSA. Although the longitudinal, circumferential and radial early diastolic strain rates (SR(E)) decreased as the severity of disease increased form moderate to severe, the late diastolic strain rates (SR(A)) were observed to increase. In the early stages of OSA, longitudinal systolic LV dysfunction is detected in addition to the diastolic dysfunction. The circumferential mechanics of the LV deteriorate in the later stages of the OSA. Despite a compensatory increase in the radial LV function in the early stages of OSA, in later stages, the LV radial function also deteriorates. The assessment of the myocardial functions using the STE method in patients with OSA with preserved LVEF has the potential to detect the subclinical LV dysfunction and might provide useful information for risk stratification.