Objective To investigate the change of corrected QT interval (QTc) of electrocardiogram (ECG) and associated risk factors of its prolongation in the elderly patients with heart failure. Methods A total of 532 old patients with left cardiac insufficiency, who had a sinus rhythm and no clear bundle branch block, were enrolled in the study in Wuxi Huishan District No.2 People′s Hospital from January 2018 to January 2021. All patients had received cardiac function assessment, ECG, and cardiac ultrasound examination ebefore the treatment. They were divided into QTc≥440 ms group and QTc＜440 ms group. Analyses were made of the changes of QTc and the risk factors of its prolongation in elderly patients with heart failure in relation to classification of New York Heart Association (NYHA), age, left ventricular ejection fraction(LVEF), left ventricular end-diastolic diameter (LVEDd), lipoprotein phospholipase A2 (Lp-PLA₂), amino-terminal brain natriuretic peptide (NT-proBNP), comorbidities of two or more diseases such as hypertension, diabetes mellitus, coronary heart disease and other heart-related diseases. SPSS statistics 21.0 was used for statistical analysis. Depending on data type, comparison between two groups was performed using t-test, χ² test or Fisher exact test. Logistic regression analysis was used to determine the risk factors of the prolonged ECG QTc. Results The patients fell into NYHA Class I-IV were 71,130, 245, and 86, and the means of QTc in the four class groups was (415.34±22.80), (423.72±38.95), (433.45±37.33) and (465.74±37.69)ms respectively (P <0.05). The mean QTc was (433.69±39.35)ms, with 207 patients in the QTc≥440 ms group [mean=(472.63±31.40) ms] and 325 in the QTc<440 ms group [mean= (408.89±18.02) ms]. The difference between the two groups was significant in age [(78.32±7.55) vs (75.03±8.07) years], LVEDd [(51.89±9.77) vs (48.95±8.69) mm], LVEF[(48.01±9.98)% vs (56.75±8.50)%], Lg(NT-proBNP) [(3.33±0.74) vs (3.03±0.68)], but not significant in ln(Lp-PLA₂)[(4.87±0.65) vs (4.79±0.84), P>0.05]. Logistic regression analysis showed that the LVEDD, LVEF, NT-proBNP and comorbidities of two or more heart-related diseases were the risk factors for QTc prolongation. Conclusion The prolonged ECG QTc in elderly patients with heart failure is correlated with cardiac insufficiency, and heart-related diseases and cardiac structural change are the risk factors.