There is evidence that episodes of obstructive sleep apnea and the occurrence of hypoxemia lead to nocturnal myocardial ischemia, and that treatment of OSA with continuous positive airway pressure ventilation reduces the occurrence of nocturnal myocardial ischemia. A Japanese survey found that the relative risk of ischemic heart disease (IHD) in patients with OSAHS was 1.2 to 6.9 times higher than that in the normal population; 35% to 40% of patients with IHD had an AHI ≥10, whereas 23.8% of patients with OSAHS had IHD.Another study found that 50% of patients with severe OSAHS suffered from coronary artery disease, and nearly 30% of patients with OSAHS who Myocardial ischemia occurs during sleep, especially during REM sleep, and ECG may show accelerated heart rate, decreased QRS amplitude, and ST-segment downshift. The ST-segment downshift disappears when treated with CPAP. Since coronary atherosclerotic heart disease is closely related to OSAHS, and OSAHS is often accompanied by coronary heart disease susceptibility factors such as obesity, hyperlipidemia and hypertension, coronary heart disease patients should pay attention to exclude the possibility of the existence of OSAHS.The mechanism of coronary heart disease complicating OSAHS may be related to the following factors; repeated hypoxia causes damage to the endothelium of the coronary arteries, and lipids are deposited in the subendocardium; erythrocytes increase, blood viscosity increases, and blood viscosity increases, and blood viscosity increases, and blood viscosity increases. In patients with OSAHS, red blood cells increase, blood viscosity increases, blood flow is slow, and platelets are easy to aggregate on the surface of the damaged endothelium to produce thrombi, causing coronary artery stenosis or occlusion. Epidemiologic data show that sleep apnea is related to myocardial infarction. On the one hand sleep apnea is an independent predictor of myocardial infarction. On the other hand myocardial infarction is also a risk factor for aggravating sleep apnea. In particular, myocardial infarction aggravates cyclic breathing and central apnea in the presence of prolonged circulation time and congestive heart failure. Possible mechanisms of association of sleep apnea with coronary heart disease; repeated hypoxemia and increased sympathetic activity due to apnea play a very important role in the formation of atherosclerosis; in addition, the immediate and long-term effects of repeated upper airway obstruction, changes in heart rate and blood pressure changes in coronary blood flow and intrathoracic pressure; and increased plasma cellulose concentration in the early morning and abnormalities of the coagulation mechanism in patients with OSAHS.