Pericardial effusion in lung cancer may be caused by tumor metastasis, hypoalbuminemia and pericarditis. 1. Tumor metastasis: Lung cancer cells can metastasize to the heart and invade pericardium, causing cancerous exudation of pericardium, resulting in pericardial effusion. 2. Hypoalbuminemia: lung cancer is a kind of consumptive disease, patients often suffer from malnutrition and hypoalbuminemia due to reduced appetite, and low albumin level will also lead to leakage of fluid in blood vessels, causing pericardial effusion. 3. Pericarditis: Lung cancer patients may suffer from pericarditis due to microbial infections such as viruses and bacteria, and the inflammation leads to the increase of pericardial exudate and causes pericardial effusion. Lung cancer patients with pericardial effusion should go to the hospital in time to improve the examination and give targeted treatment after clarifying the cause of the disease.