BACKGROUND AND AIMS: Lipoprotein (a) [Lp(a)] is a genetically regulated lipoprotein particle that is an independent risk factor for coronary atherosclerotic heart disease. However, the correlation between Lp(a) and left ventricular ejection fraction (LVEF) in patients with myocardial infarction (MI) has been poorly studied. The present study investigated the correlation between Lp(a) and LVEF, as well as the impact of Lp(a) on long-term mortality in patients with MI. METHODS: Patients who underwent coronary angiography resulting in MI diagnosis between May 2018 and March 2020 at the First Affiliated Hospital of Anhui Medical University were included in this study. The patients were divided into groups based on the Lp(a) concentration and LVEF (reduced ejection fraction group: < 50%; normal ejection fraction group: ≥ 50%). Then, correlations between the Lp(a) level and LVEF, as well as the impact of Lp(a) on mortality, were assessed. RESULTS: This study included 436 patients with MI. The Lp(a) level and LVEF were significantly and negatively correlated (r = -0.407, β = -0.349, P < 0.001). The area under the receiver operating characteristic curve (ROC) indicated that an Lp(a) concentration > 455 mg/L was the best predictive value for reduced ejection fraction (AUC: 0.7694, P < 0.0001). The clinical endpoints did not differ based on the Lp(a) concentration. However, all-cause mortality and cardiac mortality differed based on LVEF. CONCLUSIONS: These results suggest that an elevated Lp(a) concentration predicts reduced ejection fraction and that LVEF predicts all-cause mortality and cardiac mortality in patients with MI.