Inclusion criteria

NHYA class II or III symptoms of heart failure despite receiving optimal medical therapy (see details for changes mid-trial)

Left ventricular ejection fraction of 30% or less from ischemic or nonischemic causes

Intrinsic QRS duration of 120 msec or more or a paced QRS duration of 200 msec or more

Sinus rhythm or permanent atrial fibrillation or flutter with a controlled ventricular rate (â‰_60 beats per minute at rest and â‰_90 beats per minute during a 6-minute walk test) or planned atrioventricular-junction ablation after device implantation)

Planned ICD implantation for indicated primary or secondary prevention of sudden cardiac death.