Objectives: The aim of the study was to investigate the presence of endothelial dysfunction (ED) in patients with heart failure (HF) of ischemic and non-ischemic etiology (HF-I and HF-NI) using the high resolution ultrasound peripheral artery flow-mediated dilatation test (FMD-test) with the consecutive nitroglycerin mediated dilatation test (NMD test). Plasma levels of endothelial factors: von Willebrand factor (vWF) and plasminogen activator inhibitor-1 (PAI-1), were also analyzed. The comparison of these tests as established methods for endothelial function evaluation with peripheral artery flow-mediated dilatation using the novel MR-test performed according to the FMD protocol. Material and methods: The study included 65 patients with HF (31 HF-1, 34 HF-NI, 37 males and 28 women). The average age was 72 ± 11 years, and the body mass index (BMI) 27.66 ± 4.28 kg / m2, the left ventricle ejection fraction (LVEF) 38 ± 10% and the average NT-proBNP 9305 ng / l. All patients were included during hospitalization due to acute decompensated HF, after clinical stabilization, when the symptoms and signs of congestion have completely regressed. All patients were in NYHA III class. Results: All patients with HF had significantly reduced FMD and MR-indexes, the NMD-index was normal, and the e levels of vWF and PAI-1 were elevated when compared to reference values. The FMD-index values (HF-I 4.63 ± 5.64%, HF-NI 7.54 ± 8.32%) and the MR-index (HF-I 3.30 ± 0.52%, HF-NI 5.78 ± 7.27%) were significant lower, while the vWF (HF-I 173 ± 41% N, HF-NI 136 ± 47% N) and PAI-1 levels (HF-I 3.44 ± 2.31 U / ml, HF-NI 2.09 ± 1.54 U / ml) were significantly higher in patients with HF-I when compared with the HF-NI group. The linear regression analysis indicated significant correlation between the MR-test with the results of the FMD-test and with vWF plasmatic levels. The multiregression analysis of the whole sample determined significant correlation of the MR-test with the results of FMD-testing and vWF plasma levels. The time required to perform the MR-test is significantly shorter than the time needed for the FMD-test even without adding the time needed for the NMD-test that is essential part of the high-resolution endothelial testing. Conclusion: Patients with HF have significant ED regardless the etiology. The ED is more pronounced in patients with HF-I. The result of MR flow-mediated peripheral artery dilatation testing showed ED and is in correlation with the results of ultrasound FMD-test and with vWF levels. The MR test could be the method of choice for evaluating ED in routine practice. Further research is required to confirm this indication and to test its predictive ability.