Purpose: To compare the efficacy of thrombolytic therapy (TLT) in high risk patients with acute pulmonary embolism (APE) in the first day of onset of the disease and in patients with late hospitalization (3-10 days) Materials and methods: Retrospectively were processed 56 patients with a diagnosis of high risk APE (30 men, 26 women, age 60,43±3,03 years). Patients were divided into 2 groups: Group 1 includes 30 patients who were hospitalized for 1 day from an episode of APE. Group 2 includes 26 patients with APE from 3 to 10 day before hospitalization. Each group did not differ by sex, age, body weight, comorbidities. Patients of both groups after the diagnosis of high risk APE got TLT with Alteplaseof 100 mg (10 mg i/v bolus for 1 - 2 minutes, 90 mg i/v infusion over 2 hours). All patients received similar anticoagulant therapy. Patients of both groups were examined three times: before TLT (D 0), after infusion of Alteplase during 1st day (D 1) and at discharge (15±1,3 day, D 15). Results: In both groups increased SaO2, systolic blood pressure (SBP), and decreased pulmonary pressure (PP), right ventricular (RV) size and inferior vena cava (IVC) on D1 and D15 compared to D0 (all p<0,05). SaO2, RV, IVC, PP decreased significantly in Group 1 compared to patients in Group 2 on D1, this tendency continued to D15. All results see in the Table. View this table: Conclusion: The effectiveness of thrombolysis in patients of Group 1 was significantly better than in group 2. In the absence of clear criteria for the effectiveness of TLT in patients with high risk APE, the positive dynamics of RV function (size of RV, IVC, PP) and SaO2, remain simple and reliable criteria for evaluation of TLT in patients without invasive methods of treatment.