Objective To explore the characteristics of myocardial injury in patients with acute myocardial infarction(AMI)complicated by pleural effusion and its effect on long-term prognosis.Methods It was a prospective single-center study.Patients with AMI who were admitted to hospital within 15 days from symptom onset and performed echocardiography and cardiac magnetic resonance imaging(CMR)during hospitalization were consecutively enrolled and assigned to the with-pleural effusion group and the without-pleural effusion group according to the echocardiography result.Baseline data,cardiac magnetic resonance myocardial injury index and echocardiography characteristics were compared between the two groups.The occurrence of major adverse cardiovascular and cerebrovascular events(MACCE)was recorded through outpatient follow-up and telephone follow-up,including all-cause death,re-infarction,revascularization,rehospitalization for congestive heart failure and stroke.Cox regression analysis was performed to analyze influencing factors of all-cause death.Results Among 211 patients,31(14.7%)patients had pleural effusion and 180(85.3%)had no pleural effusion.Compared with the group without pleural effusion,the left ventricular end-diastolic diameter was larger,and left ventricular ejection fraction assessed by echocardiography was lower in the group with pleural effusion(P＜0.05).There were no significant differences in infarct size,left ventricular end-diastolic volume,left ventricular end-systolic volume,left ventricular ejection fraction and the presence of microvascular obstruction and intramyocardial hemorrhage between the two groups in CMR(all P＞0.05).At a median follow-up of 31 months,MACCE occurred in 43(20.4%)patients,and there was no significant difference between the two groups(χ2=3.160,P=0.075).Six cases(2.8%)had all-cause death.The incidence of all-cause death was higher in the group with pleural effusion than that in the group without pleural effusion(9.7%vs.1.7%,P<0.05).There was no significant difference in the incidence of other adverse events between the two groups(P＞0.05).Multivariate Cox regression analysis showed that advanced age and presence of pleural effusion were independent risk factors of all-cause death during follow-up.Conclusion Patients with AMI combined with pleural effusion have more severe myocardial injury and higher all-cause mortality.