Lung cancer pericardial effusion plus pleural effusion breathlessness is caused by the effusion causing extrusion on related tissues, such as lungs and pericardium, which affects the normal expansion of the lungs and produces pulmonary stasis, which is manifested as dyspnea. Lung cancer is a common primary malignant tumor of the lungs, and a series of complications, such as pericardial effusion and pleural effusion, may occur with the progression of the disease. After the occurrence of pleural effusion, excessive pleural effusion will affect the thoracic and lung expansion activities, triggering the patient to reduce ventilation, manifesting dyspnea, which may induce respiratory failure in severe cases. After producing pericardial effusion, a small amount or slow accumulation of fluid, the patient may have no obvious symptoms, a large amount of pericardial effusion when the heart diastolic capacity is significantly reduced, can not effectively return the venous blood produced by the lungs to the left heart, resulting in the occurrence of pulmonary siltation, the rate of gas exchange decreases, the patient will appear hypoxia, manifested as chest tightness, shortness of breath and so on. It is recommended that patients seek timely medical attention when symptoms of breathlessness occur to avoid delaying their condition.