Obstructive sleep apnoea (OSA) is common worldwide and is associated with cardiovascular disease. Endothelial dysfunction (ED) is regarded as a crucial step in disease development and has been demonstrated in peripheral vasculature in OSA population. However the effect of ventilatory dysfunction on myocardial perfusion is unknown. I performed comprehensive assessment of endothelial function in moderate to severe OSA subject compared with helthy and hypertensive controls, using flow mediated dilatation (FMD), laser Doppler flowmetry (LDF), flow cytometry in addition to studying vascular elastic properties. I also performed myocardial contrast echocardiography (MCE) and real time three-dimensional echocardiography (RT3DE). All these tests were repreated after 6 months of continuous positive airway pressure (CPAP) therapy. I demonstrated endothelial dysfunction in the peripheral circulation and coronary circulation as well as cardiac remodeling in OSA. However, I did not note a significant change in the indices of arterial stiffness and in the flow cytometric analysis. I noted marked improvement in the peripheral and coronary endothelial dysfunction after OSA subjects were treated with CPAP therapy for 6 months. In summary, micro- and macro-vascular dysfunction exists in otherwise healthy moderate to severe OSA subjects and improves with effective CPAP therapy. These findings may have strong clinical and prognostic implications.