Cardiac Resynchronization Therapy (CRT) is a widely accepted treatment that has led to improved clinical outcomes for patients with refractory congestive heart failure (CHF), systolic dysfunction, and wide QRS duration. However, it requires implantation of an expensive device ($30,000) and about 1/3 of patients do not have clinical improvement. Inadequate amounts of LV dyssynchrony or suboptimal lead placement may limit clinical response. Dual-Source computed tomography (DSCT) allows for subtle detection during myocardial contraction for assessing LV dyssynchrony, and can also assess coronary venous anatomy and scar burden. Thus DSCT may be the ideal noninvasive modality to predict response to CRT.

Inclusion Criteria:

• Older than 18 years of age
• Ability to provide informed consent
• Planned CRT implantation
• NYHA Functional Class II-IV heart failure
• Echo Ejection Fraction less than or equal to 35%
• QRS duration greater than or equal to 120 ms
• Normal or mildly reduced kidney function (estimated serum creatinine less than or equal to 1.5 mg/dL or less than or equal to 1.3 mg/dL for diabetic subjects on metformin
• For diabetic subjects on glucophage (metformin) they will be required to stop glucophage (metformin) for at least 48 hours after the administration of contrast.

Exclusion Criteria:

• Known allergy to iodine or iodinated contrast
• Chronic persistent atrial fibrillation
• Pregnancy or unknown pregnancy status
• Subjects on glucophage (metformin) therapy that are unable or unwilling to discontinue therapy for 48 hours after CT scan
• Known inadequate venous access for appropriate IV caliber placement
• Iodinated contrast administration within the past 48 hours
• Subjects who cannot hold their breath for 10-15 seconds

Outpatient or inpatient heart failure patients scheduled for CRT implantation