https://www.medypharmacy.com/all-the-information-you-need-to-know-about-pde5-inhibitors/

PDE-5 inhibitors are a class of drugs commonly used to treat erectile dysfunction (ED) and, in some cases, pulmonary arterial hypertension (PAH). They work by blocking the enzyme PDE-5, which is responsible for breaking down a molecule called cGMP. cGMP helps relax smooth muscle and dilate blood vessels, which is essential for increasing blood flow to the penis during sexual arousal, resulting in an erection. By inhibiting PDE-5, these drugs increase cGMP levels and enhance the effects of nitric oxide, which in turn improves blood flow.