Background Spontaneous reperfusion (SR) was associated with significant myocardial salvage, decreased mortality rates, better clinical outcomes, and lower incidences of major adverse cardiovascular events. It was found that apelin inhibited thrombin-induced and collagen-induced platelet activation and aggregation. This study was carried out to assess whether serum apelin correlates with SR of the infarct-related coronary artery in ST-elevation myocardial infarction (STEMI) patients. Patients and methods Blood samples were obtained on admission in 280 consecutive patients with STEMI before primary percutaneous coronary intervention. Blood chemistry and apelin levels were tested. Coronary arteriography and echocardiography were performed after admission. Results Frequencies of the patients with preinfarct angina, history of smoking, and pathoglycemia were higher in the non-SR group than in the SR group (P = 0.03, 0.001, and 0.002, respectively). Peak values of plasma troponin-I and frequencies of the patients with Killip 2-3 were significantly higher in the non-SR group (P < 0.05, respectively) compared with the SR group. Left ventricular systolic and diastolic functions improved markedly in the SR group compared with the non-SR group. Gensini scores were lower in the SR group than the non-SR group (P = 0.02). Serum apelin was significantly higher in patients with SR compared with patients with non-SR (0.82 +/- 0.34 vs. 0.35 +/- 0.22 ng/ml, P = 0.04). A cut-off value of 0.75 ng/ml had a predictive value of 77% to identify patients with SR. In the non-SR group, patients who died in the hospital had much lower apelin levels compared with those who survived (P < 0.001). Apelin level in the high thrombus load group was much lower compared with the other group (P < 0.001). Apelin level in the group undergoing successful reperfusion was much higher than that in the group without successful reperfusion (P < 0.001). Conclusion Patients with SR have better cardiac systolic function and improved diastolic function. An increased serum apelin level is an independent and novel predictor of SR for STEMI patients. Copyright (c) 2019 Wolters Kluwer Health, Inc. All rights reserved.