Patients with an EF greater than 50% and a regional mechanical delay of >= 65ms (an indication of mechanical dyssynchrony) will receive an implantable cardioverter defibrillator (ICD) with a special pacing feature. When the feature is active, the device wil pace the left ventricle to target improved pump efficiency. Patients will have the feature active for 4 months and inactive for 4 months. The order will be randomized and the patient will not know whether the pacing is active or not. Echocardiography, biomarkers, exercise testing, quality of life (QOL) testing and device information will be used to compare the patient's status while the feature is active vs. inactive.