The Echocardiography guided Cardiac Resynchronization Therapy (EchoCRT) study, a prospective, randomized, double-blind, international, multicenter clinical trial of its kind will randomize more than 1,250 patients with heart failure, already receiving current standard pharmacological therapy, with a narrow QRS width (<130ms) and echocardiographic evidence of left ventricular dyssynchrony. All patients will be implanted with the Biotronik Lumax HF-T CRT-D device with Biotronik Home Monitoring. The Home Monitoring data will be used in a pre-specified analysis to evaluate the frequency and duration of irregular heart rhythms. Patients will be followed for a mean duration of 24 months. The trial is being conducted at approximately 125 investigational centers worldwide, including sites in Australia, Canada, Israel, Europe and the US. GE echocardiography equipment will be utilized throughout the EchoCRT study and GE, as a clinical cooperation partner to Biotronik in this study, will provide training and technical support in order to reduce data variability and ensure optimal reliability of outcomes. Biotronik is the sole sponsor of the EchoCRT study being conducted under an investigational device exemption granted by the FDA.