How does Viagra work and how long does it last? Buy Viagra Online 100 Mg Buy Viagra Online 100 Mg. You may have questions related to how Viagra works and how long it lasts in your body. These questions and others are answered below. How does Viagra work? Viagra decreases erectile dysfunction (ED) symptoms by helping you get and keep an erection. Erections happen when a protein called cyclic guanosine monophosphate (cGMP) is released, causing more blood to flow into your penis. Then, another protein called phosphodiesterase-type 5 (PDE-5) breaks down cGMP, stopping the erection. In people having difficulty with erections, PDE-5 may work too quickly. Viagra works by blocking PDE-5 from working. This way, blood flow to the penis can occur and not be stopped by PDE-5. This also widens your blood vessels to allow more blood to flow into your penis. If you have more questions about how Viagra works, talk with your doctor or pharmacist.