Background: Because obstructive sleep apnea (OSA) was once thought to be a condition exclusively affecting men, women with OSA were frequently underdiagnosed and undertreated in comparison to men. Consequently, this study aimed to study, the deleterious effect of sever obstructive sleep apnea on left ventricular functions (Systolic & Diastolic) in female patients. Patients: This case-control study was carried out at both Cardiology Department and chest department (sleep disorder & breathing unit), Faculty of Medicine, Zagazig University in the duration from August 2023 to February 2024. Included 32 patients were subdivided into 2 groups, Group I: Included 16 females with Severe Obstructive Sleep Apnea Syndrome as cases group. Group II: Included 16 healthy females similar gender and age as control group. Results: There are no significant different in demographic character of studied groups P value ( ≥ 0.05). E/e' ratio was significant higher in Group I compared to Group II. PASP was significant higher in Group I compared to Group II. There was no significant difference in EF by SIMPSON between Group I and Group II . GLS was significant less negative in Group I in compared to Group II. Conclusion: We found that the sever cases of OSA were assosciated with subtle systolic and diastolic LV .