Pulmonary arterial hypertension can be seen in various diseases. The first major category is arterial pulmonary hypertension. Patients may have idiopathic arterial pulmonary hypertension, familial pulmonary hypertension, and arterial pulmonary hypertension caused by related diseases. Such as collagen vascular disease, portal hypertension, HIV infection, drug or toxin-induced thyroid dysfunction, myeloproliferative disorders, splenectomy, and hemoglobinopathies can also lead to arterial pulmonary hypertension. Venous pulmonary hypertension is mostly associated with left heart system diseases, such as left atrial and left ventricular heart diseases, left heart valvular diseases. Conditions like chronic obstructive pulmonary disease, interstitial lung disease, and sleep apnea related to hypotension also lead to pulmonary hypertension. Another category is chronic thrombotic or thromboembolic pulmonary hypertension. For instance, proximal or distal pulmonary artery thromboembolism, parts such as tumors, parasites, and foreign objects can also cause pulmonary embolism, thereby causing thromboembolic pulmonary hypertension.