Heart failure (HF) is the most common nosology encountered in clinical practice. Its incidence and prevalence increase exponentially with increasing age and it is associated with the increased mortality, more frequent hospitalization and decreased quality of life. An initial approach to the treatment of HF patients with reduced left ventricular (LV) systolic function and left bundle branch block (LBBB) was implantation of device for cardiac resynchronization therapy using biventricular pacing. This has resulted in long-term clinical benefits such as improved quality of life, increased functional capacity, reduced HF hospitalizations and overall mortality. However, conventional cardiac resynchronization therapy (CRT) is effective in only 70% of patients. And the remaining 30% of patients are non-responders to conventional CRT. Cardiac conduction system pacing is currently a promising technique for these patients. Particularly, His bundle pacing (HBP) has been developed to achieve the same results. According to other studies HBP has shown greater improvement in hemodynamic parameters comparing with conventional biventricular CRT. But, nevertheless, there are significant clinical troubles with HBP, especially high pacing threshold. In this regard, in 2017, the left bundle branch pacing (LBBP) was developed, which demonstrated clinical advantages compared to conventional biventricular CRT. Also, since 2019, left bundle branch pacing-optimized CRT (LBBPO CRT) has been used in clinical practice. These methods have become an alternative to HBP due to the stimulation of LBB outside the blocking site, a stable pacing threshold and a narrow QRS complex duration on electrocardiogram. A series of case reports and observational studies have demonstrated the efficacy and safety of LBBP and LBBPO CRT in patients with CRT indications. However, it is not enough data about impact of CRT with LBBP and combined CRT with LBBP and LV pacing on myocardial remodeling, reducing mortality and complications. According to our hypothesis, CRT with LBBP and combined CRT with LBBP and LV pacing compared with conventional biventricular pacing will significantly improve the clinical outcomes and reverse myocardial remodeling in patients who are non-responders to biventricular CRT with HF, reduced LV ejection fraction and with indications to CRT devices with defibrillator function (CRT-D) or one of the CRT-D leads replacement.