Objective:To observe influence of preinfarction angina pectoris (PAP)on primary ST elevation acute my-ocardial infarction (AMI).Methods:A total of 280 patients with primary ST elevation AMI received coronary angi-ography (CAG)within 24h after symptoms occurred,and they received ECG and QRS scoring on hospitalization. According to PAP or not,patients were divided into PAP group (n=102)and non PAP group (n=178).According to attack to CAG time,patients were divided into early stage group (<2h,n=60),mid-term group (2~6h,n=150)and advanced stage group (6~24h,n=70).Results:QRS score of PAP patients [(2.4±2.4)scores]was sig-nificantly lower than that of non PAP patients [(3.2±3.0)scores],percentage of high QRS score in PAP group (8.0%)was also significantly lower than that of non PAP group (18.4%),P<0.05 both.In early stage group, there was no significant difference in QRS score [(2.0±1.8)scores vs.(2.6±2.8)scores,P=0.35]between PAP and non PAP patients;The QRS score of PAP patients [(2.0±2.1)scores]was significantly lower than that of non PAP group [(3.0 ±3.0)scores]in mid-term group,P=0.03;in advanced stage group,the QRS score all signifi-cantly rose in PAP patients [(4.1 ±3.3)scores]and non PAP patients [(5.5±2.9)scores],P=0.13;QRS score gradually rose along with onset time prolonged in non PAP group.Conclusion:Preinfarction angina pectoris can de-lay progress of acute myocardial infarction and expand therapeutic window of reperfusion.