Erectile Dysfunction 

ED can occur because of problems at any stage of the erection process. An erection is the result of increased blood flow into your penis. Blood flow is usually stimulated by either sexual thoughts or direct contact with your penis.

When a man is sexually excited, muscles in the penis relax. This allows for increased blood flow through the penile arteries, filling two chambers inside the penis. As the chambers fill with blood, the penis grows rigid.

An erection ends when the muscles contract and the accumulated blood can flow out through the penile veins.