Obstructive sleep apnea (OSA) is a common condition in patients with cardiovascular diseases (CVD). The first line treatment of OSA is continuous positive airway pressure (CPAP), which reduces daytime sleepiness and improves quality of life in sleep-clinic based populations. However, in the cardiac populations, the majority of OSA subjects do not report daytime sleepiness. To date, there is not enough evidence to draw the conclusion that all CVD patients should be investigated for OSA and subsequently be treated with CPAP. The current article focuses on the available research evidence addressing the impact of CPAP on the cardiovascular consequences of OSA in both clinic- and population-based cohorts.