The action of Viagra is based on smooth muscles relaxation and blood flow increase to cavernous body. Viagra enlarges the blood-vessels of cavernous body at the sexual excitement. As a result the blood flow increases making it possible to achieve normal erection. The effect of this preparation was introduced in 1992 when the pharmaceutical company “Pfizer” had conducted trials of preparation containing sildenafil. The scientists tried to create the preparation to increase the blood flow…