EDN1 and endothelial dysfunction: There were no significant changes in the concentration of endothelin-1 in the blood, which did not depend on the severity of the disease but reached several times higher than the control group at 2.51–3.32 times (p < 0.001), which may have negative consequences in terms of the appearance of long-standing COVID-19 in the future from the cardiovascular system, or any organ and/or system where the vascular endothelium suffers most (formation of endothelial dysfunction).