You can have an erection once dead

A death erection (sometimes referred to as "angel lust") is a post-mortem erection which occurs when a male individual dies vertically or face-down – the cadaver remaining in this position. During life, the pumping of blood by the heart ensures a relatively even distribution around the blood vessels of the human body. Once this mechanism has ended, only the force of gravity acts upon the blood. As with any mass, the blood settles at the lowest point of the body and causes edema or swelling to occur; the discoloration caused by this is called lividity.