从时代周刊上找的一小段。
How sex affects the body
When a man is sexually excited, the penis fills with more blood than usual. The penis then expands and hardens. This is called an erection. After the man is done having sex, this extra bloods flows out of the penis back into the body. The erection goes away. If an erection lasts for a long time (more than 6 hours), it can permanently damage your penis. You should call a doctor immediately if you ever had an erection that lasts more than 6 hours.
Some conditions and medicines interfere with this natural erection process. The penis cannot fill with enough blood; the man cannot have an erection. This is called erection dysfunction if it becomes a frequent problem.
During a sex, your heart works harder, therefore sexual activity may not be advisable for people who have heart problems. Before you start any treatment for erection dysfunction, ask your doctor if you heart is health enough to handle the extra blood of having sex.. if you have chest pains, dizziness or nausea during sex, stop having sex and immediately tell your doctor you have this problem.