BACKGROUND AND OBJECTIVES: QT dispersion (QTd) is defined as the difference between the maximum and minimum QT interval in any of the 12 leads of the surface ECG. QTd has been shown to reflect regional variations in ventricular repolarization. Ischemic dilated cardiomyopathy (DCM) may lead to more spatial and temporal dispersion in ventricular repolarization than idiopathic DCM. The purpose of this study was to determine the difference of QTd between patients who had ischemic and idiopathic DCM. MATERIALS AND METHODS: The study population included 30 patients with ischemic DCM and 30 with idiopathic DCM. All standard 12-lead ECGs were examined prospectively by two observers who were unware of the patient's details. RESULTS: QTd in ischemic DCM was significantly higher than that in idiopathic DCM (63+/-32 vs. 44+/-26 msec, p=0.012) and JTd in ischemic DCM was significantly higher than that in idiopathic DCM (48+/-21 vs. 36+/-22 msec, p=0.036). Results did not change when Bazett's QTc and JTc was substituted for QT (QTcd:69+/-33 vs. 52+/-28 p=0.039) and JT (JTcd:56+/-21 vs. 41+/-25 p=0.043). CONCLUSION: Ischemic DCM has increased spatial inhomogeneity of repolarization probably due to more regional myocardial damages compared with idiopathic DCM. The value of QT dispersion as an easily accessible, non-invasive method in predicting the risk of life threatening arrhythmia and overall mortality in patients with dilated cardiomyopathy must be confirmed in prospective trials.