Lack of breath is a manifestation of dyspnea, which can be caused by many reasons, mostly seen in respiratory system diseases and cardiovascular system diseases. 1. Respiratory diseases can be seen due to the decline in resistance, by viruses, bacteria, mycoplasma and other pathogens, resulting in diffuse inflammatory reaction of the lungs, manifested as airway mucosal congestion, edema and inflammatory secretion exudation changes, and even blockage of the airway, accompanied by the contraction and spasm of the smooth muscle of the bronchial tubes, usually appear in the manifestation of dyspnea. 2. Can also be seen in the cardiovascular system diseases, such as congenital heart disease, heart valve disease, resulting in the emergence of the left heart failure, this time there will be acute pulmonary edema, resulting in airway obstruction, caused by lifting the breathlessness of dyspnea symptoms. In addition, there may be other reasons for dyspnea, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or therapy.