So far, CPAP is the standard treatment for patients with moderate to severe OSA. CPAP could improve airway patency, daytime sleepiness, functional status, blood pressure, metabolic abnormalities and quality of life. In our study, we enrolled 24 non-sleepy OSA and 30 sleepy OSA to study the four-week CPAP effect. The results showed the apnea-hypopnea index, hypoxia, arousal, sleepiness and fatigue could be corrected with CPAP treatment in both groups. However, CPAP could only lower risk factors for cardiovascular disease, like blood pressure, epinephrine, norepinephrine and CRP, in sleepy OSA. Our finding supported that CPAP effect was not similar in the subgroups of severe OSA, so CPAP effect should be studied in every subgroup of OSA patients before it's applied. Till now, there's no literatures reported if CPAP treatment would decrease the morbidity and mortality of AMI.