This study was designed to predict the response and prognosis after cardiac re synchronization therapy(CRT) in patients with end-stage heart failure(HF). Card iac resynchronization therapy improves HF symptoms, exercise capacity, and left ventricular(LV) function. Because not all patients respond, preimplantation iden tification of responders is needed. In the present study, response to CRT was pr edicted by the presence of LV dyssynchrony assessed by tissue Doppler imaging. M oreover, the prognostic value of LV dyssynchrony in patients undergoing CRT was assessed. Eighty-five patients with end-stage HF, QRS duration >120 ms, and le ft bundle-branch block were evaluated by tissue Doppler imaging before CRT. At baseline and six months follow-up, New York Heart Association functional class, quality of life and 6-min walking distance, LV volumes, and LV ejection fracti on were determined. Events (death, hospitalization for decompensated HF) were ob tained during one-year follow-up. Responders(74%) and nonresponders(26%) had comparable baseline characteristics, except for a larger dyssynchrony in respon ders (87±49 ms vs. 35±20 ms, p< 0.01). Receiver-operator characteristic curve analysis demonstrated that an optimal cutoff value of 65 ms for LV dyssynchrony yielded a sensitivity and specificity of 80%to predict clinical improvement an d of 92%to predict LV reverse remodeling. Patients with dyssynchrony ≥65 ms ha d an excellent prognosis(6%event rate) after CRT as compared with a 50%event r ate in patients with dyssynchrony< 65 ms(p< 0.001). Patients with LV dyssynchron y< 65 ms respond to CRT and have an excellent prognosis after CRT.