We know of the need to pump blood to the penis to make this hard, in order to have sexual intercourse. Due to certain physical conditions this can be impossible to achieve. However due to the development by Pfizer of their product Viagra these conditions can be overcome.

Viagra was originally developed and trialled as a medication for hypertension (high blood pressure). At some stage in these trials it was discovered that men were experiencing erections. This discovery was to change the course of the development of their product. It was found that Viagra worked by causing the smooth muscle in the blood vessels to relax, increase the flow of blood, also to lower blood pressure. Sildenafil, the active ingredient in Viagra, is a PDE5 inhibitor; and it is this that specifies an increase in blood flow to the penis. When a man is sexually aroused his penile arteries relax and enlarge. At the same time Viagra causes the veins that remove blood from the penis compress, acting as a valve, thus they are restricting the flow of blood from the penis causing an erection. Previously it had been thought that erectile dysfunction was purely psychological but the development of Viagra refutes this. We now know that the nerves and blood vessels play a key role. If the nerves and blood vessels do not operate correctly dysfunction occurs, this malady can now be rectified by the correct use of Viagra.