Background:Patients with heart failure (HF) have abnormal endothelial function. Although use of a continuous flow left ventricular assist device (CF-LVAD) results in significant hemodynamic improvement, the effects on systemic endothelial function are unclear.Methods and Results:Eighteen HF patients with CF-LVAD implantation were included in this prospective observational study. We measured reactive hyperemia index (RHI) before and after CF-LVAD implantation to evaluate sequential changes in endothelial function. Patients were followed clinically for the occurrence of adverse cardiovascular events, a composite of death, thrombosis, bleeding, HF, renal failure, and arrhythmia. Preoperative RHI was 1.77±0.39. Early in the postoperative period (7–14 days after operation) RHI significantly decreased to 1.19±0.31 (P<0.001, compared with preoperative RHI). At first and second follow-up (4–6 weeks and 3–7 months after operation) RHI remained lower at 1.48±0.50 (P=0.030) and 1.26±0.37 (P=0.002), respectively, compared with preoperative RHI. The decrease in early postoperative RHI relative to preoperative RHI was significantly associated with adverse cardiovascular events after CF-LVAD (age-adjusted risk ratio for 0.25 decrease in RHI, 1.35; 95% confidence interval: 1.13–1.62, P=0.001).Conclusions:Peripheral endothelial function had a significant and persistent decline up to 5 months following implantation of CF-LVAD, and this decline was associated with adverse cardiovascular events. These findings may provide insight into some of the vascular complications following CF-LVAD in HF patients. (Circ J 2015; 79: 770–777)