Aim To evaluate the effect of perindopril on the endothelial function and levels of endothelial dysfunction markers in groups of patients with heart failure with preserved (HFpEF) and mid-range (intermediate) left ventricular ejection fraction (HFmrEF).Material and methods 40 patients with HFpEF (n=20) and HFmrEF (n=20) were evaluated. At baseline, parameters of the morpho-functional state of large blood vessels and of microvessels were evaluated with photoplethysmography, and levels of E-selectin and endothelin-1 (ET-1) were measured. The patients were prescribed perindopril, and after 12 months of treatment, photoplethysmographic parameters and endothelial dysfunction markers were determined again.Results After 12 months of the perindopril treatment, improvements in the endothelial function of both large blood vessels and microvessels were noted. The phase shift increased from 10.1 to 10.9 ms in the HFpEF group (р=0.001) and from 8.35 to 9.65 ms in the HFmrEF group (р=0.002). Furthermore, the occlusion index increased from 1.45 to 1.75 in patients with HFpEF (р=0.004) and from 1.5 to 1.75 in patients with HFmrEF (р=0.010). The Е-selectin concentration decreased in both groups, from 57.25 to 42.4 ng/ml (р=0.00008) and from 40.5 to 35.7 ng/ml (р=0.010) in patients with HFpEF and HFmrEF, respectively. The ET-1 concentration decreased from pg/ml (р=0.010) in patients with HFpEF whereas in patients with HFmrEF, there was no significant change in the ET-1 concentration after 12 months of the perindopril treatment.Conclusion At 12 months, the endothelial function improved and E-selectin and ET-1 levels decreased in patients with HFpEF and HFmrEF.