Cardiac resynchronization therapy (CRT) has shown improvement in mortality and morbidity in patients with left ventricular systolic dysfunction and congestive heart failure. Additionally in CRT patients it has been demonstrated that optimizing paced/sensed atrioventricular (AV) and interventricular (V-V) timings leads to immediate hemodynamic benefits and further improves cardiac function. Recent studies have shown that optimal paced/sensed AV and V-V delays change over time, which raises the question of how often optimization should be repeated. Thus, frequent re-optimization of these delays might be beneficial for maintaining significant improvement of cardiac function. However, it remains to be evaluated whether timing optimization may be beneficial on patients who have received CRT for a number of years and are now having the CRT device replaced.

• This is a prospective, randomized, and multicenter study
• Patients who have received a replacement St. Jude Medical(SJM) CRT device, either CRT-P or CRT-D, within the last two weeks post CRT replacement will be considered for enrollment in the study.
• Baseline measurements will be performed at the time of enrollment.
• Patients are followed up to 12 months post CRT replacement with data collected at 3, 6, 9 and 12 months post CRT replacement.
• Patients will be randomized at enrollment to either Group 1 (use of SJM algorithm to optimize programming) or Group 2 ("Control").

Inclusion Criteria:

• Patient underwent a CRT replacement within the last two weeks, triggered by either the elective replacement indicator (ERI)/end of life (EOL), or by receiving a CRT-D device as an upgrade from a CRT-P device.
• Patient has received an FDA approved SJM CRT device as a replacement to the old CRT device within the last two weeks.
• Patient has the ability to complete a 6-minute hall walk without any assistance.
• Patient is willing to provide written informed consent.
• Patient has the ability to independently comprehend and complete a QOL questionnaire.
• Patient is geographically stable and is willing to comply with the required follow-up schedule.

Exclusion Criteria:

• Patient had paced/sensed AV and/or V-V delay optimization using QuickOpt before CRT replacement.
• Patient had any paced/sensed AV and/or V-V delay optimization within 3 months before CRT replacement.
• Patient has an ability to walk ≥ 450 meters (≥ 1476 feet) in 6 minutes.
• Adequate patient's echocardiography/Doppler images will not be available.
• Patient is expected to receive a heart transplant during the duration of the study.
• Patient has an epicardial ventricular lead system (Active or Inactive).
• Patient has limited intrinsic atrial activity (≤ 40 bpm).
• Patient has persistent or permanent atrial fibrillation (AF).
• Patient has 2° or 3° heart block.
• Patient's life expectancy is less than 1 year.
• Patient is less than 18 years old.
• Patient is pregnant.
• Patient is on IV inotropic agents 1 month prior to CRT replacement.