Evaluation of Resynchronization Therapy for Heart Failure (EARTH)

Inclusion Criteria (for Greater and Lesser EARTH): Patient must answer "yes" 1. Does the patient require an ICD or an ICD replacement? 2. Does the patient have a documented LVEF less than or equal to 35% measured in the previous 6 months (without major concomitant clinical event)? 3. Does the patient have a QRS duration \< 120 ms? 4. Is the patient in sinus rhythm? 5. Was the six-minute walk test distance less than 400 meters and limited by heart failure symptoms? Exclusion Criteria: Patient must have answered "NO" to all of the exclusion criteria 1. Does the patient have: * Indication for permanent ventricular pacing? * Chronotropic insufficiency? * Second or third degree AV block, either persistent or intermittent? * A pacemaker or an ICD which is paced in ventricular chamber more than 5% of the time? 2. Does the patient have a reversible cause of LV dysfunction such as post-partum cardiomyopathy, tachycardia induced cardiomyopathy, acute myocarditis or acute toxic cardiomyopathy (including acute alcoholic)? 3. Did the patient have myocardial infarction or cardiac surgery in the 6 weeks preceding the pre-implant visit? 4. Does the patient have a moderate or severe cardiac valve stenosis? 5. Is the patient's capacity to walk is limited by reasons other than heart failure symptoms (e.g., angina, intermittent claudication, severe lung condition or arthritis)? 6. Does the patient have severe coexisting illnesses making survival \> 6 months unlikely? 7. Is the patient pregnant and/or nursing? 8. Is the patient unable or unwilling to consent or to comply with follow-up requirements? 9. Is the patient participating in another clinical study potentially interfering with the present trial? 10. Does the patient have a resynchronization system in place?