Maintaining an erection should not be a problem for a healthy individual - normally, an erection should last till ejaculation (assuming that this takes a reasonable length of time) or till the stimulation stops. If maintaining an erection is a problem for you, it could be a sign of some health problem. However, most men have trouble getting or maintaining an erection at some point in their lives. This is usually only temporary, and may be due to stress, disinterest, or other psychological or environmental factors. However, if the problem continues and becomes a regular occurrence, you should consult your doctor. You will probably need to visit a specialist to determine what the problem is, as the issue is quite complex.
Cardiovascular disease is a common cause of erectile dysfunction, particularly in cases where an erection is attained, but does not last long enough for intercourse or ejaculation to be possible. The underlying cardiovascular problem could be interfering with your ability to keep blood in the penis, which is essential for an erection. Whatever the cause may be, there is a good chance that it can be fixed, if not permanently, then at least temporarily, during intercourse. Meanwhile you will also need to work on the underlying health problem if there is one.
answered by G R