Viagra 50mg is used to adult men erectile dysfunction, also known as impotence. It happens when a man can not get or keep a hard, erect panis suitable for sexual activity. Erecticle dysfunction (ED) is inability of men to attain and maintain an erect penis with sufficent rigidity to allow sexual intercourse. This medicine work by helping to relax to blood vesseles in penis, allowing blood to flow in to penis when you sexual exited.