The aim of this study was to evaluate whether the clinical benefit of cardiac resynchronization therapy(CRT)can be prospectively predicted by means of the baseline evaluation of left ventricular asynchrony. The reverse remodeling associated with CRT is more evident in patients with severe heart failure(HF)and left bundle branch block(LBBB)who have left ventricular asynchrony. Baseline left ventricular asynchrony was assessed in 60 patients with severe HF and LBBB by calculating the electrocardiographic duration of QRS and the echocardiographic septal-to-posterior wall motion delay(SPWMD). Left ventricular size and left ventricular ejection fraction(LVEF), mitral valve regurgitation, and functional capacity were also evaluated. The progression toward HF(defined as a worsening clinical condition leading to a sustained increase in conventional therapies, hospitalization, cardiac transplantation, and death)-was assessed during follow-up, as were the changes in LVEF after six months. During the median follow-up of 14 months, 16 patients experienced HF progression. Univariate analysis showed that ischemic cardiomyopathy, changes in the QRS duration after implantation, and SPWMD significantly correlated with events. At multivariate analysis, a long SPWMD remained significantly associated with a reduced risk of HF progression(hazard ratio: 0.91; 95%confidence interval: 0.83 to 0.99; p < 0.05). An improvement in LVEF was observed in 79%of the patients with a baseline SPWMD of > or=130 ms and in 9%of those with an SPWMD of < 130 ms(p < 0.0001). Baseline SPWMD is a strong predictor of long-term clinical improvement after CRT in patients with severe HF and LBBB. The aim of this study was to evaluate whether the clinical benefit of cardiac resynchronization therapy (CRT) can be prospectively predicted by means of the baseline evaluation of left ventricular asynchrony. The reverse remodeling associated with CRT is more evident in patients with severe heart failure ( HF) and left bundle branch block (LBBB) who had left ventricular asynchrony was assessed in 60 patients with severe HF and LBBB by calculating the electrocardiographic duration of QRS and the echocardiographic septal-to-posterior wall motion delay (SPWMD Left ventricular size and left ventricular ejection fraction (LVEF), mitral valve regurgitation, and functional capacity were also evaluated. The progression toward HF (defined as a worsening clinical condition leading to a sustained increase in conventional therapies, hospitalization, cardiac transplantation, and death) -was assessed during follow-up, as were the changes in LVEF after six months. During the median follow-up of 14 months, 16 patients experienced HF progression. Univariate analysis showed that ischemic cardiomyopathy, changes in the QRS duration after implantation, and SPWMD significantly correlated with events. At multivariate analysis, a long SPWMD remained significantly associated with a reduced risk of HF progression (hazard ratio: 0.91; 95% confidence interval: 0.83 to 0.99; p <0.05). An improvement in LVEF was observed in 79% of the patients with a baseline SPWMD of> or = 130 ms and in 9% of those with an SPWMD of <130 ms (p <0.0001). Baseline SPWMD is a strong predictor of long-term clinical improvement after CRT in patients with severe HF and LBBB.