INTRODUCTION The response to Cardiac Resynchronisation Therapy (CRT) varies significantly, resulting in lack of improvement among the substantial patients proportion. OBJECTIVES To identify mechanical dyssynchrony indices with combination of myocardial viability characteristics for predicting long-term response to CRT. PATIENTS AND METHODS ViaCRT was a multicentre study coordinated by the Working Group on Echocardiography of Polish Cardiac Society. 127 patients with heart failure were assessed prospectively. Cardiac dyssynchrony indices and low-dose dobutamine response were determined by echocardiography prior to CRT. Improvement in Wall Motion Score Index (WMSI) or LVEF exceeding 20% at peak stress identified preserved contractile reserve. RESULTS After 12 months there was significantly different survival between subsets with and without viability characterised by WMSI decrease, corresponding to 1 (4.4%) and 20 (19.4%) fatal events respectively (p=0.048). The predictive value of LVEF gain at Dobutamine Stress Echocardiography (DSE) study was only significant at 6 months, with all-cause death occurring in 1 (1.6%) and 7 (12.1%) of patients with viable and non-viable myocardium respectively (p=0.029). Multivariate regression analysis identified the presence of septal flash and interventricular dyssynchrony as independent indices with the ability to predict echocardiographic response alone at 12 months. CONCLUSIONS The study demonstrated a significant relationship between left ventricular contractile reserve at DSE and long-term all-cause mortality following CRT device implantation. Conversely, the presence of septal flash and interventricular dyssynchrony but not myocardial viability were predictive of the response to resynchronisation. The results indicate that interference of multiple different mechanisms may be responsible for the general effect following CRT.