The spread of a new coronavirus infection worldwide since the end of 2019 has becomes a pandemic. Thrombotic complications are the leading cause of death in this disease. After entering the human body, the virus starts a cascade of reactions leading to the development of a cytokine storm, activation of all parts of the hemostasis and complement systems and other changes that result in disturbances in the circulation system with the development of multiple organ failures. Numerous studies have shown that a predictor of a severe course of COVID-19 is a sharp increase of D-dimer concentration in the blood and rise of some other markers of hemostasis activation. Based on the pathogenesis, the developed schemes for the prevention and treatment of COVID-19 severe complications include low molecular weight heparins (LMWH) which are also recommended for an outpatient COVID-19 patient. The prescription of low molecular weight heparin, the duration of their use and doses should be decided on the basis of a risk assessment of factors for each individual patient in combination with laboratory monitoring.