Background Sleep apnea syndrome (SAS) is a common yet largely underdiagnosed comorbidity in heart failure(HF).Different predictors and specific clinical characteristics might help to identify patients at risk of developing this condition. Aim This study aimed to investigate the prevalence of moderate to severe SAS and its predictors in patients with HF.Method It was a cross-sectional study including 80 patients with stable HF. Polygraphy and echocardiography were performed for all patients.The patients were stratified into two groups based on AHI: Group 1 (G1): Patients with moderate to severe SAS AHI?15/ and Group 2 (G2): patients without SAS, AHI? 5/h.Results SAS was diagnosed in 83% of patients mainly obstructive 69%.Moderate to severe SAS was diagnosed in 44% of patients. Its occurrence was significantly associated with higher body mass index(BMI) values(p=0.001),higher neck circumference (NC) (p=0.024) and higher abdominal circumference (AC) (p=0.015).There was no difference between the two groups in comorbidities. Nocturnal apnea (p=0.025), snoring ( p=0.049), daytime sleepiness (p=0.045), and memory impairment (p=0.048) were significatly more common in G1. Echocardiographic data showed a higher posterior left ventricular wall thickness (LVWT) and lower Tricuspid annular plane systolic excursion (TAPSE) in G1 (p=0.020,p=0.039).Multivariate analysis revealed a positive and statistically significant association of moderate to severe SAS with LVWT(OR=1.12)TAPSE(OR=1.03),BMI (OR=1.02),NC (OR=1.01),and AC (OR=1.052).Conclusion Our study showed a high prevalence of moderate to severe SAS in HF mainly obstructive, and it was associated with Left ventricular hypertrophy and right ventricular dysfunction.