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Obstructive sleep apnoea (OSA) is highly prevalent and associated with an increased incidence of cardiovascular events. Endothelial dysfunction is the proposed causative mechanism. Continuous positive airway pressure (CPAP) is presumed to improve cardiovascular outcome in OSA. CPAP withdrawal was recently shown to lead to peripheral endothelial dysfunction. However, it is not known whether short-term CPAP withdrawal reduces myocardial perfusion in OSA.In this double-blind randomized controlled study, 45 patients with moderate to severe OSA previously adherent to CPAP were assigned to either subtherapeutic or continuing therapeutic CPAP for 2 weeks. The primary outcome was adenosine-induced myocardial blood flow (MBF) as a measure of endothelial function, assessed by 13N-ammonia positron emission tomography. Secondary outcomes were measures of dermal and renal microvascular function, morning blood pressure (BP) and heart rate.Despite return of OSA associated with significant increases in BP (+9.1 mm Hg, 95% CI +4.9 to +13.4 mm Hg,P< 0.001) and heart rate (+9.6 bpm, 95% confidence interval (CI) +4.6 to +14.6 bpm,P< 0.001), CPAP withdrawal had no significant effect on maximal myocardial perfusion capacity (hyperaemic MBF −0.01 ml/min/g, 95% CI −0.33 to +0.24 ml/min/g,P= 0.91), nor renal and dermal microvascular function.In patients with OSA, a short-term CPAP withdrawal does not lead to detectable impairment of coronary endothelial function, as has been demonstrated in the brachial artery, despite a clinically relevant increase in BP of nearly 10 mm Hg. There was also no evidence of an impairment of renal or dermal microvascular function.CPAP is suggested to reduce the vascular risk in OSA. This randomized controlled trial tested whether recurrence of OSA by therapy withdrawal has an impact on myocardial perfusion. OSA recurrence has no adverse effect on myocardial perfusion and microvascular function, despite clinically relevant increases in blood pressure and heart rate.