Severe pulmonary hypertension is the most severe grade of pulmonary hypertension, i.e., when the pulmonary artery pressure is >45 mmHg. The degree of grading is according to the severity of pulmonary artery grading, but clinically it is more according to pulmonary function grading, with reference to the American New York Heart Association cardiac function grading standards and the index of pulmonary artery systolic pressure to grading, divided into grade IV. Grade I is physical activity that is not limited and daily activities do not cause excessive dyspnea, weakness, chest pain, etc. Grade II is mildly restricted physical activity, asymptomatic at rest, and daily activities can cause dyspnea, weakness, and chest pain. Grade III is a significant limitation of physical activity, no symptoms at rest, lighter than daily activities can cause the above symptoms. Grade IV is unable to engage in any physical activity and has symptoms such as dyspnea and weakness at rest, and also has signs of right heart failure, which will be aggravated by any physical activity. Therefore, according to the functional classification, grade IV is severe pulmonary hypertension.