Heart failure is a progressive disorder in which the weakened heart is not able to efficiently pump blood throughout the body. When the body's cells do not receive enough blood, this can result in fatigue, shortness of breath, and difficulty carrying out daily activities. The left ventricular assist device (LVAD) is a device that is used to provide mechanical circulatory support to patients with end-stage heart failure who are awaiting heart transplants. Although LVAD support helps maintain the pumping ability of the heart and dramatically improves heart failure symptoms, the quality of life with LVAD support is far from ideal. It has been shown that LVAD support in selected patients may restore the failing heart enough to eliminate the need for heart transplant, but more information is needed to assess heart recovery and to guide weaning of LVAD support. Using data collected from patients who have undergone LVAD implantation, this study will attempt to better assess heart recovery and to generate criteria for identifying patients eligible for the removal of LVAD support.