In this study, we assessed the impact of COVID-19 on the course of HFmrEF by determining the biomarkers furin and NT-proBNP, questionnaires (EQ-5D-5L), and cardiac ultrasound. A comprehensive examination of 72 patients with HFmrEF (main group) and 18 apparently healthy individuals (control group). The main group was divided into two subgroups depending on the history of coronavirus disease. All patients gave their consent to participate in the study. In the group of patients with a history of coronavirus infection compared to the patients without a COVID-19 history were established: significantly higher concentrations of NT-proBNP (1002.79±215.94 pg/ml and 405.37±99.06 pg/ml, respectively, p-value 0.01), uric acid (429.08±27.01 mmol/l vs. 354.44±28.75 mmol/l, p-value 0.04) and a lower furin to NT-proBNP ratio (0.87± 0.26 and 1.38 ± 1.16, p-value 0.045) in blood serum; using the EQ-5D-5L questionnaire, a significant deterioration of quality of life indicators (64.21±3.04 points vs. 72.81±1.82 points by VAS, p-value 0.02); higher indicators of LVMMi (157.39±6.14 g/m2 and 138.68±6.02 g/m2, p-value 0.03), LA dimensions (43.74±0.95 mm and 41.12±0.85 mm, p-value 0.04) and RA dimensions (40.76±1.23 mm and 37.75±0.85 mm, p-value 0.04). Coronavirus infection in patients with HFmrEF leads to disorders of intracardiac hemodynamics and persistent negative structural changes of the heart. The ratio of furin to NT-proBNP serum levels can be used to determine the impact of the HF syndrome itself on the patients' subjective assessment of their quality of life.