Abstract： Objectives To investigate the effect of ventricular conduction delay on QTc/JT interval, left ventricular ejection fraction as well as exercise tolerance in patients with heart failure.Methods Twelve lead synchronous electrocardiogram, left ventricular ejection fraction and exercise peak oxygen consumption were investigated in 79 patients with heart failure, mean age (60 ±12)yeara, 35 patients had ischemic cardiomyopathy, 25 patients had idiopathic dilated cardiomyopathy.Sixteen patients had other unknown aetiologies.Results Patients with idiopathic dilated cardiomyopathy had longer QRS duration than those with ischemic eardiomyopathy.In patients with wide QRS had longer QT/QTc, than those with normal QRS duration, but JT intervals were similar.Left ventricular end diastolic dimension and left ventricular ejection fraction were similar between two groups.Peak VO2 was significant reduced in patients with wide QRS duration.Conclusions Ventricular activation duration has a significant effect on QTc, and peak VO2.JT interval may be suitable measurement of repolarization in such patients.Electrophysiologic approach may be a potential treatment for these patients.