Background. In decompensate heart failure, preexisting or newly developed electrical disturbance may contribute to the mechanical dysfunction, which eventually affects prognosis. Prolonged duration of depolarization presented as a wide QRS complex reflects ineffective and sometimes dyssynchronous LV contraction. Repolarization abnormality, which presents as a prolonged corrected QT interval (QTc), can be related with abnormal relaxation or rarely sudden cardiac death caused by fatal ventricular arrhythmia. Objective. We assessed whether the duration of QRS complex or QTc interval in initial electrocardiogram is related with the mortality in patients admitted with acute decompensate heart failure. Method. 12-lead electrocardiograms, which were taken on admission in the patients with acute decompensated heart failure from the KorHF registry, were analyzed. Depending on the duration of QRS complex longer than 120 msec and/or duration of QTc interval longer than 440msec, patients were divided into three groups; group 1 with no prolongation, group 2 with either of which, and group 3 with both QRS widening and QTc prolongation. Results. Among 3199 patients, who were enrolled from January, 2005 to October, 2009, QRS duration and QT interval was available in 2571 patients. Overall mortality rate was 24.8% during a mean follow up duration of 19 짹 14 months. In baseline characteristics, patients in group 3 were older (70짹14 in group 1, 70짹15 in group 2 vs. 72짹12 in group 3; p<0.001) and had lower left ventricular ejection fraction (40짹15% in group 1, 40짹16% in group 2 vs. 34짹14% in group 3; p<0.001). Levels of NT-proBNP was lower in group 1 (8268짹10192 pg/mL in group 1 vs. 8772짹9873 pg/mL in group 2, 8845짹9936 pg/mL in group 3; p=0.041). Patients in group 3 who had both wide QRS complex and prolonged QTc interval showed higher overall mortality rate (24% vs. 23% vs. 31%; p=0.044). Interestingly, there was a significant difference in survival rate among groups in non-ischemic heart disease (24% vs. 19% vs. 32%; p=0.002) while no difference was shown in ischemic heart disease (p=0.157). Readmission rate within 1 year was higher in group 3 (19% vs. 17% vs. 23%; p=0.020). QTc interval was prolonged in patients who developed ventricular fibrillation (690짹129 msec vs. 474짹86 msec, p=<0.001). However, QTc prolongation was not correlated with in-hospital sudden cardiac death (p=0.144). Conclusion. In acute heart failure, patients who has both wide QRS complex and prolonged QTc interval has a poor prognosis, especially in non-ischemic heart diseases.