Thickening of the pulmonary valve refers to the increase in the thickness of the pulmonary valve due to various reasons, causing the corresponding conditions, which will cause abnormal valve activity, and the common causes include pulmonary hypertension, infections, and immune system factors. 1. Pulmonary hypertension: the most common cause of pulmonary valve thickening, prolonged increase in pulmonary artery pressure, resulting in abnormal contraction of the pulmonary artery, changes in blood flow around the pulmonary valve, resulting in thickening of the valve. 2. Infections: Bacterial (hemolytic streptococcal) infections can damage the pulmonary valve, causing inflammation of the valve, which further leads to thickening. 3. Immune system disorders: Immune system disorders (rheumatism, etc.) can lead to allergic inflammation, which can cause thickening of the valve when it becomes involved. Obvious thickening of the pulmonary valve, abnormal valve activity, affecting the blood supply to the pulmonary artery, need to consult a doctor for observation and standardized treatment under the guidance of the clinician.