Primary percutaneous coronary intervention (pPCI) is the most effective reperfusion therapy in the treatment of ST-elevation myocardial infarction (STEMI). Although the infarct-related artery of STEMI patients is effectively revascularized during pPCI, effective reperfusion in the myocardial tissue may not be achieved. This condition is called the no-reflow (NR) phenomenon. FGF-21 is a circulating hormone-like molecule primarily secreted by the liver and has been proven to be the main metabolic regulator of glucolipid metabolism and insulin sensitivity. The aim of this study was to investigate the predictive effect of FGF-21 on the development of the NR phenomenon in STEMI patients undergoing pPCI.