Used primarily to treat erectile dysfunction by enhancing blood flow to the penis during sexual stimulation. It works by inhibiting an enzyme that regulates blood flow, allowing for stronger and more sustained erections. Also prescribed for pulmonary arterial hypertension, as it helps relax blood vessels in the lungs, reducing strain on the heart and improving exercise capacity. Commonly taken orally in tablet form, effects typically begin within 30 to 60 minutes and last several hours.