Background: Medications induced QT prolongation could cause ventricular arrhythmia, torsade de pointes, and death. Objective: The purpose of this study was to evaluate the magnitude of QTc interval prolongation as a result of levofloxacin treatment in patients admitted to cardiology wards. Methods: This was a cross-sectional study conducted in the coronary care units and general wards of the Imam Ali Heart Hospital in Kermanshah, Iran. The QTc interval was determined at baseline and after 72 hours of levofloxacin administration. Changes in the QTc interval before and after the levofloxacin prescription were determined. Results: The mean age of recruited patients was 63.26 ± 14.56 years. More than 80% of patients who received levofloxacin experienced QTc prolongation. The QTc interval was increased significantly after levofloxacin administration (15.68 ± 26.84 milliseconds) (P<0.001). These changes remained significant after excluding medications with QTc lengthening properties (P<0.001). Conclusion: Treatment with levofloxacin in patients with heart disease increases the risk of QT prolongation.