LODO-CRT is a multicenter prospective study enrolling HF patients with conventional indication to CRT (symptomatic stable NYHA class III-IV on optimized drug therapy, QRS≥120 msec, left ventricular (LV) dilatation, LVEF≤35%) is designed to assess the predictive value of LV contractile reserve (LVCR), determined through DSE, in predicting CRT response during follow-up. Assessment of CRT effects will follow two sequential phases: in phase 1 CRT response end-point is defined as left ventricular end-systolic volume (LVESV) reduction ≥ 10% at 6 months; in phase 2, both LVESV reduction and clinical status via a clinical composite score will be evaluated at 12 months follow-up. Predictive value of LVCR will be compared to other measures, such as LV dyssynchrony measures, through adjusted multivariable analysis. For the purpose of the study, target patient number is 270 patients (with 95% confidence, 80% power, α≤0.05).