Dr. Jonathan Hsu and Dr. Eric Adler are conducting a research study to find out more about how implantable cardiac defibrillator (ICD) settings can be adjusted to improve patient cardiovascular health and quality of life. Patients are being asked to participate in this study if they have a history of heart failure and have or are scheduled to be implanted with a BIOTRONIK ICD that is capable of closed loop stimulation (CLS). CLS is a device setting that works with the cardiovascular system to optimize their heart rate during physical activity. This study is comparing BIOTRONIK's CLS setting to a standard accelerometer setting, which also is able to adjust the heart rate by movement sensors, when necessary. This study has been initiated by Dr. Hsu and Dr. Adler and is financially supported by BIOTRONIK, Inc. There will be approximately 15 participants in this trial.