Background: Undiagnosed obstructive sleep apnoea (OSA) is a risk factor for postoperative atrial fibrillation (POAF) as well as for heart disease in general. This necessitates screening during preoperative assessment to facilitate the implementation of strategies to minimise the postoperative risk. Overnight polysomnography is the "gold standard" for the diagnosis of OSA but may be impractical during preoperative assessment, and so questionnaires may be useful for screening OSA. The Berlin Questionnaire (BQ) and Epworth Sleepiness Scale (ESS) are two of the widely prescreening tools for persons who may suffer from sleep disorders. Thus, screening for and treating OSA as part of the routine preoperative evaluation of cardiac surgical patients may be a useful strategy for preventing POAF.