Cardiac resynchronization therapy (CRT) is one of the most important advances in the treatment of patients with heart failure (HF). This therapy, also known as biventricular pacing, utilizes pacemaker leads to synchronize the contraction of the walls within the left ventricle (LV) and the contraction of the left and right ventricles. Many randomized trials have conclusively demonstrated that CRT improves symptoms, LV structure and function, hospitalization rates, and survival in appropriately selected HF patients. Nonetheless, approximately 30% of CRT patients will be "non-responders" because they will not demonstrate the expected clinical and/or echocardiographic improvement following therapy. A critical component of assessing CRT efficacy during the optimization clinic will be the use of a novel method of body surface electrocardiographic mapping under development by Medtronic, called the ECG Vest. In this proposal, we describe a research study to assess the potential benefit of using the ECG Vest as part of a CRT optimization strategy on clinical and echocardiographic outcomes (heart size and function) of patients receiving standard clinical care in the UHVC CRT Optimization Clinic.