A phosphodiesterase type-5 inhibitor, often shortened to PDE-5 inhibitor, is a drug used to block the degradative action of phosphodiesterase type-5 on cyclic GMP in the smooth muscle cells lining the blood vessels supplying the corpus cavernosum of the penis. These drugs are used in the treatment of erectile dysfunction and were the first effective oral treatment available for the condition. Because PDE-5 is also present in the arterial wall smooth muscle within the lungs, PDE-5 inhibitors have also been found to be effective for the treatment of pulmonary hypertension, a disease in which blood vessels in the lungs become abnormally narrow.

Two drugs in this class have been approved for the treatment of Pulmonary Hypertension:

• Sildenafil Citrate
• Tadalafil