Abstract Body (Do not enter title and authors here): Heart failure (HF) is a global epidemic claiming millions of lives worldwide. Unloading the heart of end-stage HF patients via left ventricular assist devices (LVADs) is used not only as a bridge to transplantation but also as a bridge to recovery in certain selected patients. To date, assessment of patients’ recovery from HF is based on clinical and symptomatic evaluation. The use of non-invasive biomarkers that monitor the remodeling/reverse remodeling associated with HF progression/recovery is still lacking. In this study we applied mass spectrometry-based quantitative redox proteomics to identify serum biomarkers to monitor both the progression of HF and its recovery after LVAD treatment. A fingerprint of reversed behavior at the protein and at the oxidized Cys peptide level has been discovered when comparing HF and LVAD patients. HDL proteins related to lipid metabolism were decreased in HF samples and increased in LVAD patients. In addition, a number of inflammatory proteins showed a decrease in LVAD samples and an increase in HF samples. In particular APOA4, C7, F2 or SAA2 discriminated between HF and LVAD patients. A pool of peptides containing specific oxidized Cys residues showed an inverse relationship in HF as opposed to LVAD samples. Oxidized Cys-containing peptides derived from Albumin, IGK and IGG1 discriminated HF from LVAD samples. Discriminatory sensitivity and specificity were enhanced by using a combination of the proteins APOA4, C7, F2 and the above-mentioned peptide derived from Albumin. Responders and non-responders could also be separated by proteins such as APOA4, and Cys-oxidized peptides, such as the ones derived from Albumin or IGK mentioned above. This is the first study to apply redox proteomics to explore the protein profile of the LVAD unloaded human heart. These data suggest that HDL plays an important role in LVAD recovery and that a specific group of peptides is associated with the recovery process; the mechanisms involved need further study. Our data could have important implications to the management of patients in the LVAD recovery program and could serve to identify new therapeutic targets.