AIMS: Cardiac resynchronization therapy is currently used in selected patients with end-stage heart failure. However, 30% of patients do not respond to CRT. The aim of our study was to find echocardiographic (TDI), electrocardiographic (QRS interval and electric distance between right and left catheter), clinical (6MW test) or autonomical (HRV) parameters able to predict responsiveness to CRT. MATERIALS AND METHODS: 47 patients (mean age 74+/-10 years) with end-stage heart failure, symptomatic, with left ventricular (LV) ejection fraction less than 35% and QRS 120 ms, underwent CRT. RESULTS: At thirteen months follow up, all clinical and echocardiographic parameters significantly improves (EF p<0.001; LVED volume p<0.001; 6MWT p<0.001; max delay TDI p<0.001; HRV p<0.05; Right-left distance p<0.05). A positive response was documented in 31/47 (67.4%) patients who presented an increase in LVEF > or = 5 units. There was a significant difference of LVED diameter (p<0.05) and HRV (p<0.05) between responders and non responders. Receiver-operating curve analysis showed that a positive response to CRT may be predicted in patients with LVED diameter <67 mm (with a sensitivity of 77% and a specificity of 88%). CONCLUSIONS: Our results confirm the clinical improvement obtained by CRT in end-stage heart failure patients as well as the limited value of QRS duration and intraventricular dyssynchrony as predictor of clinical recovery after CRT. While a most-advanced clinical stage of disease (HRV) without an advance left ventricular remodeling (LVED diameter) demonstrated to predict response to CRT, with sensitivity of 77% and specificity of 88%.