Question: what are phosphodiesterase 5 inhibitors?
Answer: PDE 5 inhibitors stop a particular enzyme (phosphodiesterase type 5 [PDE5]), found in blood vessel walls, from working properly. PDE5 helps control blood flow to the pulmonary arteries. By stopping PDE5 from working, PDE 5 inhibitors (ie sildenafil and tadalafil) cause the blood vessels to relax.