Background/Aims: Acute myocardial infarction (AMI) is one of the leading causes of death in the world. However, specific diagnostic biomarkers have not been fully determined, and candidate regulatory targets for AMI have not been identified to date. Long noncoding RNAs (lncRNAs) are a class of RNA molecules that have diverse regulatory functions during embryonic development, normal life, and disease in higher organisms. However, research on the role of lncRNAs in cardiovascular diseases, particularly AMI, is still in its infancy. HOX antisense intergenic RNA (HOTAIR), a 2.2 kb lncRNA, was initially described as a modulator of HOX gene expression. Recent studies have illustrated the important role of HOTAIR in cancer progression, but few studies have reported its function in cardiac disease, including AMI. In the current study, we aimed to detect the expression of HOTAIR during AMI and to explore its function in hypoxia-induced cardiomyocyte injury in neonatal cardiomyocytes. Methods: In 50 consecutively enrolled AMI patients, we examined the serum expression levels of HOTAIR and analysed its correlation with cardiac troponin I (cTnI) expression. Another 50 age- and sex-matched subjects served as healthy controls. Next, the HOTAIR expression was detected in the serum from C57BL/6J mice subjected to coronary artery ligation and in neonatal rat cardiomyocytes induced by hypoxia. Cultured cardiomyocytes apoptosis were measured by terminal deoxynucleotide transferase dUTP nick end labelling (TUNEL) staining. A search for miRNAs that had complementary base paring with HOTAIR was performed utilizing an online software program, and the interaction between miR-1 and HOTAIR was examined using a luciferase reporter assay. Results: Our study revealed that HOTAIR expression was significantly decreased in the serum of AMI patients compared with that of the healthy controls. Similarly, we observed that HOTAIR was downregulated in the serum of mice subjected to coronary artery ligation and in cultured cardiomyocytes exposed to hypoxia. Furthermore, we observed that the adenovirus vector-driven overexpression of HOTAIR dramatically limited hypoxia-induced myocyte apoptosis, whereas knockdown HOTAIR by AdshHOTAIR (adenoviral short hairpin HOTAIR) exhibited the opposite phenotype. Mechanistically, we discovered that the cardioprotective function of HOTAIR is partly based on the negative regulation of miR-1. Conclusions: Taken together, the results of our study suggest that HOTAIR is a protective factor for cardiomyocytes and that the plasma concentration of HOTAIR may serve as a biomarker for human AMI diagnosis.