When a man is aroused, nerve signals are sent from the brain and around the penis. These nerve signals cause chemicals to be released. These chemicals relax muscles in the penis. Normally, these muscles are constricted so that blood cannot flow into the penis. When these muscles relax, large amounts of blood are able to enter the penis, causing an erection. An erection is reversed when another chemical (known as phosphodiesterase type 5 [PDE5]) breaks down the chemicals that caused the muscles to relax in the first place. This causes the muscles in the penis to constrict again, which results in blood leaving the penis.
viagra cialis online pharmacy pharmacy works by blocking PDE5. When PDE5 is blocked, more of the chemicals responsible for the erection remain, so the muscles in the penis do not constrict. This allows blood to stay in the penis longer, which allows the man to maintain an erection.
