Getting an erection is a team effort! Your blood vessels, nerves, body chemicals and state of mind all have to work together to make an erection happen.
The act of your penis becoming erect is caused by increased blood flow to your penis. This causes your penis to swell and become firm. So to get and keep an erection that's suitable for satisfying sex, you need good blood flow to the penis.
To find out more about what goes on inside your penis when you get an erection, click here.