Background Continuous positive airway pressure(CPAP)treatment has been proven to be effective in improving the symptoms of coexisting coronary heart disease(CHD)in patients with obstructive sleep apnea hypopnea syndrome (OSAHS). However, it is still unclear whether such improvements are linked to changes in vascular endothelial function. This research was carried out to investigate the effects of CPAP treatment on vascular endothelial function in patients with OSAHS and CHD. Methods Thirty-six patients with moderate or severe OSAHS and CHD undergoing three months of CPAP treatment were recruited for this study. The changes in their morning plasma nitric oxide(NO)and endothelin(ET) levels, NO/ET ratio, total ischemic burden(TIB)of the myocardium, apnea hypopnea index (AHI), and minimal and mean pulse oxygen saturation(SpO2)were compared and analyzed before and during CPAP treatment. Results Compared with the plasma levels of ET[(51.39±11.69)ng/L] and NO[(36.67±11.86)μmol/L], NO/ET(0.71±0.14), AHI(32.4±7.9), minimal SpO2[(68.9±11.4)% ], and myocardial TIB[(66.29±16.37)mm min]before treatment, there were significant decreases in ET [(33.41±10.03)ng/L](P<0.05), increases in NO[(59.89±10.26)umol/L] and NO/ET(1.79±0.38)(P<0.01), decreases in AHI(1.9±0.5), and increases in minimal Sp02[(90.6±1.8)%](all P<0.01)and myocardial TIB[(36.42±10.87)mm min](P<0.05 )after three months of CPAP treatment. Conclusion CPAP treatment may play an vascular endothelial dysfunction and myocardia mportant role in the improvement and protection of ischemia in OSAHS patients with CHD.