REsynchronization reVErses Remodeling in Systolic Left vEntricular Dysfunction (REVERSE)

Inclusion Criteria: * Subjects with previously symptomatic heart failure but no current symptoms (New York Heart Association (NYHA) Class I, Stage C) or subjects with mild heart failure that only sometimes interferes with daily activities (NYHA Class II) * Subjects with a QRS of 120 ms or more (The QRS interval is a measurement of how the electrical signal involved in a heart beat travels/conducts through the ventricles. A wide QRS (120 ms or more) suggests that there is a conduction problem (or block) in the ventricles). * Subjects with a left ventricular ejection fraction less than or equal to 40%. (The left ventricular ejection fraction (LVEF) is a measurement of how well the left ventricle pumps blood out to the rest of the body. The higher the LVEF the more blood the ventricle is pumping.) * Subjects with a left ventricular end diastolic dimension (LVEDD) greater than or equal to 55. (The left ventricular end diastolic dimension (LVEDD) is a measurement of heart size taken during an echocardiogram that is one indication of the health of the left ventricle.) Exclusion Criteria: * Subjects who are pacemaker dependent (heart would not beat without the help of an implanted device to pace it). * Subjects with heart failure that severely limits daily activities (NYHA Class III) or subjects with severe heart failure with symptoms while resting (NYHA Class IV). * Subjects hospitalized due to heart failure within past 3 months.