Complex chemistry processes manage all this activity. Erection occurs when nitric oxide acts on the smooth muscles surrounding the penile arteries, acts on an enzyme, which then relaxes the smooth muscles, and an erection begins. The enzyme called phosphodiesterase type 5 (PDE-5) blocks muscle relaxation. So the way a pro-erection medication like Viagra works is to inhibit PDE-5 so that it does not block relaxation. This enhances (prolongs) the effect of vascular relaxation, which encourages blood flow, producing and maintaining an erection. Accept the complexity of your sexual response and appreciate that it is relaxation (not performance demands) that facilitates erection. So now you understand why pelvic muscle relaxation is important for good erections.