Cardiac resynchronization therapy (CRT) is a well-established interventional treatment for heart failure patients. The major rationale for CRT is based on the concept of correction, through pacing of the delayed asynchronous contraction of the lateral wall of the left ventricle, in patients suffering from left bundle branch block (LBBB). The aim of the study was to investigate long-term mortality and morbidity of classic and new electrocardiographical markers in patients with CRT. We investigated negative prognostic value of new ECG markers like: pathological preimplantation axis, increase in total QRS amplitude in V3 during biventricular pacing, apical LV-paced QRS morphology, LV-paced QRS duration, different LBBB definitions. A longitudinal cohort study was performed: 590 patients that had undergone CRT device implantation in the 1st Department of Cardiology, Interventional Electrocardiology and Arterial Hypertensionin Kraków, between February 2006 and December 2014 were analysed retrospectively. The endpoint was determined for June 2016. Outcomes were categorized according to two endpoints: 1. all-cause mortality or urgent heart transplantation and 2. all-cause mortality or heart failure hospitalization.