The FDA has approved Revatio for the treatment of pulmonary arterial hypertension (PAH). This is a rare, progressive lung disease that causes high blood pressure in the arteries of the lungs. The condition can lead to heart failure and death. It is a phosphodiesterase type-5 (PDE5) inhibitor. It works by relaxing the blood vessels in the lungs, which lowers blood pressure and makes it easier for the heart to pump blood.