Pulmonary artery is mostly a pathological and clinical state caused by the dislodgement of a deep vein thrombus in the lower extremity and the occurrence of embolism in the pulmonary artery and its branches, blocking the blood supply to the tissue. Because of pulmonary embolism, more right than left lungs and more lower than upper lungs, less common pulmonary embolism will ride across the bifurcation of the pulmonary artery. Therefore, left lateral position is recommended when pulmonary embolism occurs. Left lateral position not only reduces the obstruction of breathing, but also prevents the patient from further asphyxia. However, for patients with pulmonary embolism, the best approach is absolute bed rest, because without normal restoration of blood flow, once activity may aggravate the patient’s symptoms of respiratory distress and lack of oxygen, and may even lead to asphyxia. Therefore, for patients with pulmonary embolism, the left lateral position can be used for mild cases, and for severe cases, they must lie on their back and avoid activities.