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The QRS represents the simultaneous activation of the right and left ventricles, although mostof the QRS waveform is derived from the larger left ventricular musculature. Although normalQRS duration is <100 millisecond (ms), its duration and shape are quite variable from patient topatient in idiopathic dilated cardiomyopathy (IDCM). Prolongation of QRS occurs in 14% to 47%of heart failure (HF) patients. Left bundle branch block (LBBB) is far more common than rightbundle branch block (RBBB). Dyssynchronous left ventricular activation due to LBBB and otherintraventricular conduction blocks provides the rationale for the use of cardiac resynchronizationtherapy with biventricular pacing in patients with IDCM. Fragmented QRS (fQRS) is a markerof depolarization abnormality and present in significant number of the patients with IDCM andnarrow QRS complexes. It is associated with arrhythmic events and intraventricular dyssynchrony.The purpose of this manuscript is to present an overview on some clinical, echocardiographic andprognostic implications of various QRS morphologies in patients with IDCM.