Subjects were recruited if their healthcare provider decided that they needed treatment with a special Internal Cardiac Defibrillator (ICD) called a biventricular ICD. The investigators did this study to see if part of the nerve organ, called the sympathetic nervous system, may be responsible for the improvement seen in patients that receive biventricular pacing. The investigators had three ways to measure sympathetic nervous activity: 1) by using a special blood sample, 2) by monitoring heart rhythm, and 3) by performing a special heart scan.