Cardiac resynchronization therapy (CRT) improves myocardial performance in patients with heart failure (HF) and left bundle-branch block (LBBB). Tissue Doppler echocardiography (TDE) has already been used to guide the selection of candidates for CRT. The objective of this study is to correlate the effects of CRT on left ventricular (LV) systolic function with wall motion synchrony assessed by TDE. High frame TDE data were obtained in 15 patients (mean age = 68.9 years, 11 men) with LBBB (QRS = 163 +/- 13 ms) to derive temporal intraventricular horizontal asynchrony indexes, expressed as the time difference at the onset of shortening between the septum and the lateral (S-L) and antero-inferior (A-I) walls, and measure the amount of delayed longitudinal contraction (DLC) within the LV. All measurements were made at baseline, 24 hours after implantation, and at 1 year of follow-up. The results show that LV ejection fraction (EF) increased from 25 +/- 6.2% at baseline to 36.9 +/- 7.9% at 1 year, and was strongly related to DLC, expressed either by time duration (DLCd, r =-0.51; P < 0.0001) or percent of the basal segments (%DLC, r =-0.50; P < 0.001). New York Heart Association functional class, which decreased from 3.6 +/- 0.5 to 2.3 +/- 0.8, was correlated with %DLC (r = 0.50) and DLCd (r = 0.48, P < 0.001). Weaker correlations were found between LVEF and S-Li (r =-0.40) and between NYHA and S-Li (r = 0.40). It is concluded that DLC was the best among intraventricular asynchrony indexes in predicting increases in LVEF after CRT. DLC may be useful to identify responders to CRT.