Viagra, also known as sildenafil, is a selective phosphodiesterase-5 inhibitor that is widely used in the treatment of pulmonary hypertension because of its selective intrapulmonary vasodilating effect and its low effect on body circulation pressure, which does not cause hypotension. The mechanism of action of sildenafil is to reduce pulmonary artery pressure by selectively inhibiting pulmonary vascular endothelial phosphodiesterase-5, which leads to relaxation of vascular smooth muscle and diastole of pulmonary artery vessels. In addition, sildenafil also has the effect of stimulating the release of nitric oxide in the body, which also has a vasodilatory effect; this drug also has the effect of enhancing the contractility of the right heart. Through the above principles, sildenafil is commonly used in the treatment of pulmonary hypertension. However, due to its vasodilating effect, its main side effects include headache, facial flushing, rhinorrhea, nausea, blurred vision, etc., which should also be taken seriously and the dosage should be adjusted according to the situation.