What is Erectile Dysfunction? Erectile dysfunction, also known as ED, is when a man can't get or keep a strong enough erection for sex. But, what happens next? These two long, cylindrical chambers inside the penis are called the corpora cavernosa. They have a lot of blood vessels and tissues inside, as well as one main artery in each one. When you get excited, your brain sends chemical signals to the blood vessels in your penis. This causes them to dilate or open, letting blood flow throug...