Objective:To investigate the clinical efficacy of alteplase combined with heparin in the treatment of acute moderate- and high-risk pulmonary thromboembolism and its effects on arterial blood gas analysis and myocardial enzyme level.Methods:Seventy-eight patients with acute moderate- and high-risk pulmonary thromboembolism who received treatment in Dongyang People's Hospital from January 2015 to January 2022 were retrospectively included in this study. They were divided into observation ( n = 39) and control ( n = 39) groups according to different treatment methods. The control group was treated with heparin, while the observation group was treated with alteplase based on heparin. All patients were treated for 7 days. Clinical efficacy as well as arterial blood gas analysis, myocardial enzymes, pulmonary artery pressure, and tricuspid annular plane systolic excursion pre- and post-treatment were compared between the two groups. Results:The total response rate in the observation group was significantly higher than that in the control group (94.87% vs. 76.92%, χ2 = 5.18, P < 0.05). After treatment, the partial pressure of carbon dioxide in the observation group was significantly lower than that in the control group [(36.24 ± 5.12) mmHg vs. (44.25 ± 3.78) mmHg, 1 mmHg = 0.133 kPa, t = 7.86, P < 0.05]. After treatment, the partial pressure of oxygen in the observation group was significantly higher than that in the control group [(78.82 ± 5.1) mmHg vs. (71.23 ± 4.89) mmHg, t = 6.66, P < 0.05]. After treatment, lactate dehydrogenase, creatine kinase, and creatine kinase isoenzyme in the observation group were (107.42 ± 15.45) U/L, (37.21 ± 10.84) U/L, and (12.28 ± 3.54) U/L, respectively, which were significantly lower than (189.94 ± 21.20) U/L, (65.42 ± 6.57) U/L, and (19.29 ± 3.08) U/L in the control group ( t = 19.64, 13.89, 9.33, all P < 0.001). After treatment, the pulmonary arterial pressure in the observation group was significantly lower than that in the control group [(32.24 ± 3.86) mmHg vs. (37.79 ± 5.17) mmHg, t = 5.37, P < 0.001]. Tricuspid annular plane systolic excursion in the observation group was significantly higher than that in the control group [(14.07 ± 1.27) mm vs. (12.63 ± 1.16) mm, t = 5.22, P < 0.001]. Conclusion:Ateplase combined with heparin has an obvious effect on acute moderate- and high-risk pulmonary thromboembolism. It can improve arterial blood gas analysis and reduce myocardial enzyme levels.