22 patients with (OSAS) obstructive sleep apnea syndrome were divided into two groups: patients with OSAS and without arterial hypertension, and OSAS with hypertension. The effect of CPAP (continuous positive airway pressure) on the left ventricular function was evaluated using 2D and Doppler echocardiography. Systolic left ventricular function (ejection fraction) was normal in all patients. The decrease in peak mitral flow velocity during early diastole E (m/sec), the increase of atrio-systolic contraction A (m/sec), the increase in E/A and prolonged isovolumic relaxation time (IVRT) was observed in the both groups at the beginning of the study. After three month treatment with CPAP the increase in the ratio E/A, 1.38 + 0.23 m/sec vs 0.98 + 0.28 (p < 0.05) and a reduction in IVRT, 79 + 6.8 milisec vs 91.3 + 6.3 (p < 0.05) in the group with OSAS and hypertension was observed. In the group with OSAS and without hypertension only a statistically significant reduction in IVRT was observed, 77.8 + 5.4 vs 83.7 + 5.15 milisec p < 0.05.