Based on recent research on the pathophysiology and diagnostic techniques of pulmonary arterial hypertension (PAH) and the understanding of the clinical manifestations, new treatments and preventive features of various types of PAH, the clinical classification criteria for pulmonary circulatory hypertension (PH) were revised at the 3rd World PAH Conference held in 2003. The revision maintained the basic framework and spirit of the 1998 Evian classification, and updated the susceptibility and associated factors of PAH. Compared with the old classification, the new classification of PH as a tool is more comprehensive and easier to operate, which is helpful for clinicians to assess the condition and develop standardized treatment and preventive measures, and is also easier to promote. The new classification method has the following features: 1. Stop using the diagnostic name of “primary pulmonary hypertension (PPH)” Studies in the past 20 years suggest that appetite suppressants, connective tissue disease, portal hypertension or human immunodeficiency virus (HIV) infection can also cause pulmonary vascular lesions, and their pathological changes and clinical features are similar to those of PPH. Because the diagnostic name “secondary” PAH is not only unhelpful for diagnosis and treatment, but also confusing, it was discontinued in the Evian classification developed at the Second World Conference on PAH. The diagnostic name of PPH has been used in clinical and scientific research for more than 50 years and is widely known and accepted by the medical community, so it is still retained. In recent years, it has been found that abnormal bone morphogenetic protein receptor II (BMPR II) is an important cause of PPH, and the name PPH is obviously no longer applicable. Therefore, in the new classification, the diagnostic name of idiopathic pulmonary arterial hypertension (IPAH) was used instead of PPH. 2. Addition of genetic-based classification of familial pulmonary arterial hypertension About 50% of familial pulmonary arterial hypertension (FPAH) and 10% of sporadic IPAH have a genetic basis related to mutations in the gene encoding BMPRII on chromosome 2q33. However, the ectopic rate of BMPRII mutation is not high, and only 15-20% of the population carrying BMPRII mutation can develop PAH. only 70 cases of BMPRII mutation causing IPAH have been reported in the world so far. Mutations in the activator receptor-like kinase I (ALK-1) gene and 5hydroxytryptamine carrier gene are also associated with IPAH and PAH caused by a few hereditary hemorrhagic capillary dilatation disorders. 3. reclassification of pulmonary veno-occlusive disease (PVOD) and pulmonary polypoidal capillary hemangioma (PCH) In the 1998 PH classification criteria, PVOD and PCH were classified in two separate categories, with PVOD classified as pulmonary venous hypertension and PCH classified as PAH resulting from disease that directly damages the pulmonary vascular bed. subsequent studies have suggested that in both PVOD and PCH Subsequent studies have suggested that pulmonary ferritin deposition, interstitial pulmonary edema, lymphatic dilation, intimal thickening of the pulmonary arteries, mesangial smooth muscle hyperplasia and arterial plexus-like changes are present in the lung parenchyma of both PVOD and PCH, and that pulmonary edema may occur in both when treated with prostacyclin. This suggests that the two diseases may overlap. PVOD and PCH have a poor prognosis and should be considered for lung transplantation once they are diagnosed. The time of onset of PAH is related to the site of the defect, and in simple cardiac defects, PAH is more common in ductus arteriosus and ventricular septal defects. The onset of PAH is related to the site of the defect. The incidence of eisenmenger syndrome is only 3% when the diameter of the septal defect is ≤1.5 cm and the fractional flow is small, but it is 50% when the defect is >1.5 cm and the fractional flow is large. Therefore, early correction of cardiac malformations can prevent the occurrence of PAH.