Objective:To investigate the effect of continuous positive airway pressure (CPAP) on serum NO and plasma ET and myocardial structure in mini pigs with obstructive sleep apnea syndrome (OSAS).Methods: Twenty-four male mini pigs were evenly randomized into 4 groups: normal control group (group A), OSAS model group (group B), CPAP treated group (group C) and positive control group (group D).Animals in group A were not treated and those in the other 3 groups were treated with intermittent hypobaric hypoxia 6 h daily for 22 d.Animals in groups C was also given further CPAP treatment 6 h daily for 30 d.The animals in group D were raised for 30 d and were sacrificed together with those in group C; the animals in group A and group B were sacrificed simultaneously.Sleep monitoring and determination of serum NO and plasma ET were performed before execution and pathological examination of myocardial structure after execution.Results: The apnea-hypopnea index (AHI) of group C was significantly lower than those of group B and D and higher than that of group A (P<0.05); the SpO2 of group C was significantly higher than those of group B and D (P<0.05), and was similar to that of group A.The levels of NO in group A, B, C, and D were (0.221±0.062), (0.115±0.061), (0.110±0.033), (0.077±0.043) μmol/L, respectively, and the levels of ET were (40.2±4.8), (99.8±22.4), (67.1±18.5), and (103.7±30.1) pg/ml, respectively.Group C had significantly higher NO level and lower ET level compared with group D (P<0.05).The ET level in group C was significantly lower than that in group B (P<0.05).Pathological examination showed that the myocardial structure in group B, C, and D all had hypoxia and ischemia damage compared with group A; the damage in group C was slighter than that in group B and D, but severer than that in group A.Conclusion: Thirty day-treatment with CPAP can improve the sleeping indices, plasma ET and serum NO level, and myocardial structure of OSAS mini pigs.