The advantages of upgrade to cardiac resynchronisation therapy (CRT) have not been explored as carefully as the outcomes of de novo CRT implantations. Furthermore selection criteria for patients with the potential to benefit the most from this therapy are unknown. Therefore, we analyzed the long term outcome and its predictors in a real-world cohort receiving a CRT upgrade from previous pacemaker (PM) and defibrillator devices (ICD). We analyzed 86 patients (mean age 68 ± 9 years; 89% male) undergoing CRT upgrade procedures. Response to CRT as well as long term patient outcome was analyzed. NYHA class improved in majority of the patients during short term period (61%), and this trend remained constant during long term follow-up (54%). The observed all-cause mortality was 54% with mean survival of 49 ± 4 months. 11 patients underwent left ventricular assist device implantation or heart transplantation. In the multivariate analysis, only kidney function assessed by GFR (HR 0.97; 95% CI 0.95-0.99; p = 0.009) and LVEF (HR 0.92; 95% CI 0.87-0.97; p = 0.002) remain predictors for mortality. Patients who undergo an upgrade procedure to CRT demonstrate a significant response rate assessed by improvement in NYHA class, with initial baseline parameters such as LVEF and kidney function remaining significant predictors for mortality.