Sudden feeling of chest tightness, breathlessness, chest pressure, may be due to physiological factors or cardiovascular system diseases such as coronary heart disease, arrhythmia, etc., respiratory system diseases such as pulmonary embolism, pneumothorax, etc., need to carry out a comprehensive analysis to clarify the cause. 1. Physiological factors: Normal people may experience chest tightness and breathlessness after strenuous exercise, which can be relieved after stopping exercise and resting for some time. 2. Diseases of the cardiovascular system: it may be coronary heart disease, coronary artery stenosis or sudden occlusion of blood vessels, causing ischemia and hypoxia of the distal myocardium, and the collection of lactic acid and other acidic substances, which stimulate the nerves to cause chest tightness, breathlessness, and tightness of the chest; it may be cardiac arrhythmia, disorders of the heart’s electrical activity, such as premature beats, tachycardia, and so on, which cause changes in the heart’s hemodynamics, resulting in insufficient blood perfusion to the myocardium, and the emergence of symptoms such as chest tightness and breathlessness. 3. Respiratory diseases: some patients may be due to the rupture of pulmonary alveoli, gas into the pleural cavity, lung tissue atrophy, causing chest tightness, dyspnea, chest percussion is drumming, chest pressure; some patients may have lower extremity venous thrombosis, thrombus dislodgement along with the blood circulation, into the right atrium, right ventricle, and then blocked the pulmonary artery, causing chest tightness, chest pain, dyspnea, hemoptysis and other symptoms. When a sudden feeling of chest tightness, breathlessness, chest pressure to rule out physiological causes, the situation may be more critical, should be promptly to the hospital, a clear diagnosis, and according to medical advice for treatment, such as delayed condition may have cardiac arrest, respiratory failure and other risks.