Introduction: The clinical symptoms of pulmonary embolism are diverse and in some patients, pulmonary embolism can be easily overlooked and cause serious clinical consequences. Case Report: This report describes a case of acute pulmonary embolism whose first symptom was presyncope. A 23-year-old male patient presented with presyncope and dyspnea. Acute coronary syndrome and neurological disorders such as stroke and seizures were excluded by clinical history and dynamic changes in the electrocardiogram. After the diagnosis was completed with computed tomography pulmonary angiogram, the severity of acute pulmonary embolism was evaluated and then the fibrinolytic drug was given to the patient. Conclusion: This case is of guiding importance for the early diagnosis and treatment of these patients who had pulmonary embolism after long-term immobilization, which poses a potential risk for venous thromboembolism. Cardiopulmonary diseases should be highly suspected in patients with problems with basic vital signs. After evaluating the possibility of pulmonary embolism and performing a D-dimer scan, a computed tomography pulmonary angiogram should be performed as soon as possible.Additionally, the critical degree of pulmonary embolism shouldbe assessed and appropriate reperfusion and anticoagulation therapy should be administered.