What, if any, are the clinical implications of this information? OSA is more common than is generally realized. The condition clearly leads to considerable morbidity and also excess mortality. If, in addition, OSA is an independent risk factor for cardiovascular disease as has been hypothesized by some, devising preventive strategies may be of paramount importance. The study of Alonso-Fernanadez et al provides further evidence of the connection between OSA and cardiovascular disease but falls short of documenting a causative role. One of the limitations of the study is that there is a lack of evidence that any of the ECG abnormalities described by the authors are of any clinical significance. Thus, there is no information about whether the observed ST-segment depression was associated with symptoms that might be attributable to myocardial ischemia (eg, angina in the waking state). Similarly, it is not documented whether any of the patients with arrhythmias during sleep experienced palpitations or syncope while awake. The clinical significance of transient asymptomatic arrhythmias or nocturnal ST-segment depression is unclear. In addition, although patients with known valvular disease, hypertension, or recent myocardial infarction or stroke were excluded from the study, there is no information about risk factors such as dyslipidemia or cigarette smoking or any diagnostic studies such as stress tests, cardiac catheterization, or assessment of left ventricular function. Thus it is difficult to determine the prevalence of organic heart disease within the study population and whether it was comparable between study groups. It also seems unusual that the body mass index in the OSA patients was not significantly different from the other two groups, considering the high prevalence of obesity in OSA. Perhaps, despite the best efforts of the authors, the study population was preselected in a manner that could conceivably have biased the results.