Pulmonary edema is a disease in which excess fluid accumulates in the lungs, interfering with normal pulmonary ventilation and air exchange, resulting in a range of clinical symptoms. Under normal conditions, there is a balance between the production of tissue fluid (i.e., plasma exuding from capillaries to become tissue fluid) and reflux (i.e., tissue fluid being absorbed by the venous and lymphatic systems) that exists in the interstitial space of the body’s cells. In pulmonary edema, the balance of tissue fluid production and reflux in the lungs is broken for some reason, so that the lung tissue fluid cannot be absorbed by the pulmonary venous and lymphatic systems for a short period of time and accumulates in the interstitial space of the lungs. When the accumulation reaches a certain amount, it suddenly overflows into the alveoli and develops into alveolar edema. The alveoli, as an important intermediate station for oxygen, are blocked by tissue fluid at this time, which affects the body’s oxygen supply. Patients may exhibit extreme dyspnea and feel less breathless only when sitting, accompanied by blue lips, profuse sweating, and paroxysmal cough with large amounts of white or pink foamy sputum. In the early stage of pulmonary edema, patients often have symptoms such as coughing, chest tightness, shallow and rapid breathing; as pulmonary edema further develops into the alveoli, patients will have symptoms such as pale face, blue lips and severe dyspnea. Therefore, in daily life, especially for patients with poor cardiopulmonary function, regular medical checkups are needed to achieve early detection and treatment.