Objective:To investigate the clinical application value of left ventricular myocardial strain obtained by cardiac MR (CMR) in recent major adverse cardiovascular events (MACE) in patients with acute ST-segment elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PCI).Methods:From January 2020 to December 2020, a total of 163 patients successfully underwent primary PCI and underwent CMR examination within one week after surgery at Affiliated Hospital of Xuzhou Medical University. The scan sequences included rapid balance-fast field echo and late-gadolinium enhancement. CVI42 post-processing software was used to analyze and measure the left ventricular myocardial strain indices, including left ventricular global longitudinal strain (GLS), left ventricular global circumferential strain (GCS), and left ventricular global radial strain (GRS). According to the results of the 1-year follow-up after surgery, the patients were divided into the MACE group ( n=28) and the non-MACE group ( n=135). For continuous variables with a normal distribution, the t test of two independent samples was used for comparisons between groups. For continuous variables with an abnormal distribution, the variables were compared and analyzed by the rank sum test. For categorical variables, the χ 2 tests were used for between-group comparisons. Cox regression was used to analyze the prognostic value of myocardial strain on the development of MACE in patients with STEMI. The receiver operating characteristic (ROC) curve was used to analyze the diagnostic efficacy of myocardial strain parameters, and the optimal cut-off value was evaluated by calculating the Youden index. Results:The GLS, GCS, and GRS of the MACE group were (-10.4±3.3)%, [-11.9 (-14.5, -9.3)]%, and (18.3±6.3)%, respectively, and those of the non-MACE group were (-13.7±3.4)%, [-14.6 (-16.4, -11.7)]%, and (22.3±6.1)%, respectively. The difference between the two groups was statistically significant ( t/ Z=-4.71, -3.04, 3.21, P<0.05). Multivariate Cox regression analysis showed that GLS was an independent predictor of MACE (HR=1.546, 95%CI 1.180-2.027, P=0.002). The ROC curve analysis showed that GLS had the largest area under the curve (AUC) (AUC=0.754, 95%CI 0.658-0.851, P<0.001), with a cut-off value of -12.45%. Its diagnostic sensitivity was 71.4%, and the specificity was 67.4%. The value was better than that of the traditional predictor of STEMI prognosis, namely, left ventricular ejection fraction (AUC=0.680, 95%CI 0.567-0.793, P=0.003). Conclusion:GLS of CMR is an independent predictor of MACE in STEMI patients undergoing primary PCI.