Background. Obstructive sleep apnea syndrome (OSAS) is associated with cardiovascular mortality and morbidity. Several studies have reported that it affects the left ventricle; however, large randomized controlled trials are lacking. The current study aimed to summarize the association between OSAS and left ventricular (LV) structure and function. Methods. Electronic databases (PubMed, Embase, and Cochrane) and references were searched for articles published until March 2018. A systematic review and metaanalysis were performed to assess LV structure and function in OSAS patients based on echocardiography.