Background/Aim: Endoplasmic reticulum (ER) stress plays a critical role in the development of cardiac hypertrophy and heart failure. Heart failure is a crucial health problem that affects 23 million people worldwide, causes approximately 2.4 million people to be hospitalized every year in the USA, and leads to the death of more than 300,000 people. In this study, we aimed to investigate the clinical significance of ER stress markers and the predictive value of acute decompensated heart failure in patients with low ejection fraction heart failure (ADHF). Patients and Methods: This is a prospective case control study. The data included laboratory parameters pertaining to patients with ADHF in the emergency service and lipid parameters obtained during their admission to the hospital. In addition, the same parameters obtained from the control group patients with chronic heart failure (CHF) during their routine polyclinic control were recorded in the data set. Admission time to the hospital and length of hospital stay were included in the data. The levels of glucose regulated protein (GRP78), protein kinase RNA-like endoplasmic reticulum kinase (PERK), and C/EBP homologous protein (CHOP) in peripheral blood serum obtained from the patients and the control group were measured using the ELISA method. Results: Serum GRP78 concentration was lower in the HF group (p=0.003) compared to the control. The median value of serum PERK concentration in the HF group was higher than that of the control group (573 pg/ml, IQR=477.5-650 vs. 495.5 pg/ml, IQR=294-648, respectively) (p=0.001). However, there were no statistically significant differences in GRP78 and PERK serum concentrations between ADHF and CHF subgroups. Receiver operating characteristic (ROC) curve analysis showed greater area under the curve (AUC) for the serum GRP78 levels of the healthy individuals (AUC=0.748, 95% CI=0.681-0.814, p=0.0003). The serum GRP78 level was found to be 80% sensitive and 70% specific at 147.5 pg/ml (p=0.0003) for distinguishing healthy individuals from HF patients. In the ADHF subgroup, there was a moderate correlation between hospitalization time and serum CHOP concentrations (Spearman rho=0.586 and p=0.001). Conclusion: High GRP78 serum concentration may protect the patient from ER stress. In addition, the serum PERK level is high in patients with HF, whereas it is insufficient in predicting acute decompensation. CHOP may be useful in predicting the length of hospital stay in patients with ADHF.