Aim To evaluate the effect of 12-month perindopril treatment on structure and function of microvasculature (MV) in patients with chronic heart failure with preserved (HFpEF) and intermediate (HFiEF) left ventricular ejection fraction.Material and methods 30 patients with HFpEF and HFiEF were evaluated. Perindopril at a maximum tolerated dose was administered to all patients for 12 months. Changes in MV structure and function were assessed with photoplethysmography and capillaroscopy prior to the treatment onset and at 12 months, i.e., after completion of the perindopril treatment.Results The 12-month perindopril treatment was associated with improvement of the endothelial function evident as increases in the occlusion index (OI) and the phase shift (PS). OI increased from 1.45 [1.3; 1.6] to 1.8 [1.6; 2.2] (p=0.00004). PS increased from 7.1 ms [4.8; 10.2] to 9.2 ms [6.7; 13.2] (p=0.0003). Stiffness of muscular large blood vessels was decreased. Arterial stiffness index (aSI) decreased from 8.8 [6.6; 11.0] to 7.45 [6.5; 9.4] m /s (р=0.01). The perindopril treatment was associated with increased density of the capillary network at rest (р=0.008) and in tests with venous occlusion (р=0.003) and reactive hyperemia (р=0.0003).Conclusion The study showed an improvement of endothelial function associated with the 12-month perindopril therapy in patients with HFpEF and HFiEF.