Viagra (otherwise known by its non-brand-name of sildenafil) is used to treat erectile dysfunction. It functions by blocking the enzyme called phosphodiesterase 5 (PDE5), which may end erections prematurely.
Sildenafil citrate is also sold under the name Revatio and generically under other names. Viagra was developed by the pharmaceutical company Pfizer. Viagra pills are typically blue, diamond-shaped and have the words "Pfizer" on one side, and "VGR xx" the other. The "xx" stands for the dosage in milligrams.
Other sildenafil pills on the market are tadalafil (Cialis), and vardenafil (Levitra).
Sildenafil has been studied in men with ischaemic heart disease and with a wide range of other risk factors. A low incidence of serious or clinically significant adverse events, including cardiovascular events, was reported, comparable to that in patients with no known history of cardiovascular disorders.