Objective — searching for chronic heart failure (CHF) biomarkers in patients with heart failure and reduced LVEF through exhaled breath analysis by proton mass spectrometry. Material and methods. The study included 42 patients with CHF and reduced LVEF (HF-REF) and 24 patients without CHF in the control group for the period from October 2014 to April 2016. Exhaled breath samples were collected in 1L Tedlar bags (USA). Exhaled breath samples were analyzed using PTR-MS (Compact PTR-MS, «Ionicon», Austria) within 24 hours after sampling. Results. Men significantly prevailed (90.5%) in HF group compared with the control group (59.3%; p<0.0001). Previous myocardial infarction was more common in patients with CHF (p=0.021). Exhaled breath composition in patients with CHF along 36 channels of mass spectrometer differs from that in the control group. Most of these substances (n=23) were in trace amounts in exhaled breath (<1 · 10–9). Pathophysiological mechanisms of formation are known only for acetone (985 · 10–9 vs. 330 · 10–9 in patients with HF and in the control group, respectively; p<0.0001). There were correlations of exhaled acetone with LVEF, mean pulmonary artery pressure, NT-proBNP, urea, uric acid and total bilirubin. It was also found that exhaled acetone concentrations are various in patients with different NYHA functional class of CHF and higher in patients with NYHA class IV compared with patients with NYHA class II (p=0.006). ROC-analysis was performed to estimate diagnostic accuracy of exhaled acetone for diagnosis of HF-REF. AUC was 0.811 (95% CI 0.707—0.915; p<0.0001). No correlation of exhaled acetone and blood glucose was revealed. Conclusion. Exhaled breath analysis may be used as a new non-invasive screening test for HF-REF. Exhaled acetone is characterized by the greatest diagnostic value.