Sleep disordered breathing (SDB), which causes sleep deprivation, intermittent hypoxia, and negative intrathoracic pressure swings, can be accompanied by other harmful pathophysiologies relating to cardiovascular diseases (CVD), including sudden death, atrial fibrillation, stroke, and coronary artery disease leading to heart failure. Continuous positive airway pressure (CPAP) therapy for SDB has been reported to provide favorable effects such as lowered systemic blood pressure and improved endothelial function. However, in recent randomized controlled trials, CPAP has failed to demonstrate its beneficial prognostic impact on the primary or secondary setting of CVD. In this review article, we describe the characteristics of SDB complicated with CVD, the prognostic impacts of SDB in CVD, and the beneficial effects of CPAP on CVD. strate its beneficial prognostic impact on the primary or secondary setting of CVD 18, 23-27). In this review article, we describe the characteristics of SDB complicated with CVD, prognostic impacts of SDB in CVD, and beneficial effects of CPAP on CVD. Diagnosis, Definition and Classification of SDB Overnight polysomnography, which includes assessments of electroencephalogram, electrooculogram, electrocardiogram, and electromyogram, as well as the nasal and oral airflows, respiratory movement (thorax and abdominal respiratory effort), snore, oxygen saturation, body position, and sleep stage, is the gold standard test for SDB (Fig. 2) 1, 28). Apnea is the absence of inspiratory airflow for at least 10 s. Hypopnea, a decrease in airflow lasting 10 s or longer, is associated with a drop in arterial oxygen saturation and/or an electroencephalographic arousal.1, 28 The total counts of apnea or hypopnea per hour are defined as the apnea hypopnea index (AHI), and is used to determine SDB: normal, AHI 5/h; mild, 5 ≤ AHI 15/ h; moderate, 15 ≤ AHI 30/h; severe, AHI ≥ 30/h. Apnea and hypopnea are classified as obstructive or central, but they both result from an absence or reduc-Copyright©2019 Japan Atherosclerosis Society This article is distributed under the terms of the latest version of CC BY-NC-SA defined by the Creative Commons Attribution License.