The paper presents the history of a 17-year-old patient admitted to the paediatric cardiology department in a life-threatening condition with dyspnoea, blood desaturation up to 90% and chest pain. The patient contracted COVID-19 (she was not vaccinated), and additionally treated her acne with oestrogen hormonal drugs. Computed tomography of the chest revealed massive embolic changes in the pulmonary artery and its branches. After introduction of heparin under the control of activated partial thromboplastin time and then warfarin under the control of international normalised ratio (INR), regression of changes was achieved; however, the arterial vessel narrowed up to the upper lobe of the right lung. During cardiac catheterisation, the vessel was widened with a balloon and successfully opened. Follow-up echocardiography showed regression of changes, the dimensions of the right heart decreased, and the features of pulmonary hypertension disappeared. During the exercise test, she reached stage 4. After 2 months, to avoid patient exposure to radiation, follow-up magnetic resonance imaging of pulmonary vessels was performed instead of computed tomography, showing partial restoration of the artery. Currently, the patient is still taking warfarin (INR 2.5–3.5), is in good general condition and a lung scan is planned in the future.