Aim In heart failure (HF) patients with iron deficiency, cardiac electrical irregularity is a cause of arrhythmias. The aim of our study was to evaluate the effect of ferric carboxymaltose (FCM) treatment on T wave peak to end (Tp-e) interval and the Tp-e / QT and Tp-e / corrected QT (QTc) ratios that reflect the transmural dispersion of repolarization in HF patients with iron deficiency.Material and methods Forty HF patients with iron deficiency that were treated with FCM were included in our single center, observational study. Repolarization parameters on electrocardiograms recorded before and 12 wks after FCM treatment were compared. Additionally, these parameters were compared with ventricular repolarization parameters of 40 healthy age and gender matched individuals and with another group of 40 HF patients without iron deficiency.Results In the HF patients with iron deficiency, the Tp-e interval and the Tp-e / QT and Tp-e / QTc ratios before FCM treatment were 103.7±19.1 ms, 0.25± 0.04, 0.23±0.04, respectively. These values were higher compared to the healthy the group and HF group without iron deficiency (p<0.001). In the HF patients with iron deficiency, the Tp-e interval and the Tp-e / QT and Tp-e / QTc ratios after FCM treatment were lower compared to pre-treatment and similar to the HF patients without iron deficiency (89.4±18.6 ms, 0.22±0.04, 0.20±0.04, respectively; p<0.001).Conclusion FCM treatment of HF patients with iron deficiency corrects prolonged Tp-e interval and high Tp-e / QT and Tp-e / QTc ratios, which are risk factors for ventricular arrhythmias.