Introduction: Reliable and objective diagnostic tools are needed for heart failure to assist prompt intervention, diagnosis, treatment, and admission and/or discharge decisions in the emergency room. The aim of this study was to assess the treatment-associated changes in corrected QT interval in patients with decompensated heart failure in the emergency care setting. Materials and methods: Thirty-nine adult patients with known heart failure presenting to the emergency room with New York Heart Association Class III-IV decompensated systolic heart failure symptoms were included in this study. Initial and post-treatment electrocardiography recordings were examined for corrected QT interval changes. Results: Treatment of decompensated heart failure resulted in a statistically significant reduction in QT interval when compared to pre-treatment measurements: 432.3±43.3 (range, 320-508) vs. 486.3±44.1 (range, 414-600) milliseconds, p=0.001. Discussion: Monitoring corrected QT interval may represent a useful additional assessment tool that may aid in the assessment of decompensated heart failure patients in the emergency room and in the decision for admission and discharge. However, further studies are warranted.