Some reports suggest that the course of diabetes mellitus (DM) in heart failure (HF) may improve after implantation of left ventricular assist devices (LVADs). The objective of our study was to explore longitudinal changes in glycosylated hemoglobin (HbA1C) in patients with diabetes mellitus with advanced HF post-LVAD implantation. We retrospectively reviewed the records of all patients who received LVADs at our institution between 2002 and 2012 and selected those who 1) survived posthospital discharge and 2) had DM. We collected data on HbA1C before and after implantation of LVADs, daily doses of insulin, and antidiabetic drugs. Comparisons were done using Student’s t-test. A total of 50 patients met the inclusion criteria. HbA1C was 7.6 ± 1.6 before LVAD, 5.7 ± 0.9 within 3 months after the LVAD implant (p = 0.0001), 6.1 ± 1.0 (p = 0.004 in comparison with pre-LVAD level) in 3–6 months after the implant, 6.3 ± 1.0 (p = 0.01) in 6–9 months, and 5.3 ± 0.1 in 9–12 months (p = 0.002). There were no significant changes in body mass index. Favorable changes in clinical course of diabetes in patients with HF occur after the implantation of LVADs, persist for at least 1 year after the implant, and are likely associated with improved hemodynamics and metabolism after normalization of cardiac output.