Objective: This study evaluated the usefulness of cystatin C as a prognostic predictor in heart failure patients admitted to the emergency department. Methods: This study was conducted retrospectively on patients with heart failure admitted to the emergency department between January and December 2018. Patients newly and previously diagnosed with heart failure underwent both N-terminal prohormone of brain natriuretic peptide and cystatin C tests. To assess the patients’ prognosis, a poor prognosis was defined as the occurrence of one or more of the following events: intubation, admission to an intensive care unit, coronary angiography, continuous renal replacement therapy, extracorporeal membrane oxygenation, cardiopulmonary resuscitation, and death. The patients were divided into two groups based on the occurrence of these events; the characteristics between the groups with and without events were compared. Results: Seventy-four patients were included in the study analysis: 35 and 39 in the group without and with events, respectively. The number of patients with a history of diabetes, hypertension, troponin T, and cystatin C levels were significantly higher in the group with events than in the group without events (P=0.028, P=0.041, P<0.001, and P=0.002, respectively). Multiple logistic regression analyses showed that cystatin C is a significant prognostic predictor of events. Conclusion An increased cystatin C level has been shown to clinically predict a poor prognosis of heart failure patients admitted to emergency departments.