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Purpose: Cardiac Resynchronization Therapy (CRT) has become an advantageous treatment option in patients (PTS) with systolic heart failure and wide QRS complexes. The response to CRT, however, varies significantly among individuals, and different predictors of beneficial outcome have been proposed. This multicentre study sought to investigate the potential impact of myocardial viability and echocardiographic dyssynchrony parameters on CRT efficacy.Methods: 75 PTS with ischemic and non-ischemic left ventricular dysfunction undergoing CRT were included. Dyssynchrony at rest and viability during dobutamine stress test were assessed by baseline echocardiography prior implantation. The 6 week follow-up echocardiographic data were compared with regard to substantial increase of LVEF.Results: Within the total studied population, a significant increase of mean LVEF from 25% to 39% (P < 0,0001) during follow-up was observed in 37 responders (RES). This subset had also a more pronounced rise of LVEF (6%, P=0.0001) and decrease of Wall Motion Score Index (0.12, P = 0.02) at baseline dobutamine test as compared to non-responders (Non-RES). No significant difference of mean lateral-to-septal delay by tissue Doppler was observed between RES and Non-RES groups (10 ms). However interventricular dyssynchrony showed timing prolongation of 58 ms among RES in comparison to 37 ms within Non-RES (P = 0.009).Conclusions: The results of ViaCRT trial indicate that preserved contractile reserve by baseline dobutamine test is associated with significant improvement of LV systolic function at 6 week follow-up. A simple echocardiographic measurement of interventricular dyssynchrony at baseline reveals more prolonged values in patients with beneficial response to CRT.