Objective To explore the predictive value of different degrees of delirium after off-pump coronary aortic bypass grafting (OPCABG) for perioperative myocardial infarction (MI). Methods A retrospective analysis was conducted on the clinical data of patients who underwent OPCABG in the First Department of Cardiac Surgery at the First Hospital of Hebei Medical University between April 2018 and March 2024. Patients were divided into a mild delirium group, a moderate delirium group, and a severe delirium group based on the degree of delirium, and into a MI group and a non-MI group based on the occurrence of perioperative MI. Binary logistic regression analysis was used to investigate the predictive factors for secondary MI during OPCABG. The predictive value of different degrees of postoperative delirium for secondary perioperative MI was assessed using receiver operating characteristic (ROC) curves. Results A total of 436 patients were included, with 211 males and 225 females, and a median age of 51 (44.0, 57.75) years. Delirium occurred in 139 patients, with 52 in the mild delirium group, 29 in the moderate delirium group, and 58 in the severe delirium group. MI occurred in 101 patients, with 101 in the MI group and 335 in the non-MI group. Binary logistic regression analysis showed that severe delirium was an independent predictor of secondary MI during OPCABG [OR=23.979, 95% CI (11.572, 49.691), P=0.000]. ROC curve analysis revealed that the area under the ROC curve for predicting perioperative MI by severe postoperative delirium was 0.709, with a sensitivity of 0.546 and a specificity of 0.964. Conclusion Severe postoperative delirium can be used as an indicator to predict secondary MI during OPCABG.