Most men have problems with erections from time to time. But when this happens more than half of the time, then ED is present. ED can happen when health problems limit blood flow or damage nerves in the penis. ED can also be caused by stress or emotional reasons. ED can be an early warning of a more serious illness. Heart disease, high blood pressure and high blood sugar can all cause ED. Finding and treating the cause(s) of your ED can help your overall health and well-being.