An erection is a surprisingly complex process. It begins in the brain, which sends chemical messages to the nerves in the penis. The blood vessels relax, blood flows in and then, high pressure traps the blood within the corpora cavernosa. It all occurs within seconds and then, voila, an erection!

Unfortunately, that process can be complicated by all kinds of factors, including anatomy, illness, or something as simple as the wrong vibe. This infographic looks at some of the key factors that affect the ability to get - and stay - hard, and provides some handy tips on what men can do to ensure they're always ready to perform at their best.

Source: Institute for the Study of Urologic Diseases