Ask the doctor: Tracking down the possible causes of fainting
Q. After my mother fainted several times, her doctor referred her to a cardiologist. What might be wrong with her heart, and what tests should she expect?
A. The most common reason people faint is that the heart slows down instead of speeding up. In response, the blood vessels widen, blood pressure falls, and the brain doesn't get enough blood. Fainting is the body's way of restoring blood flow to your brain. Strong emotion, intense pain, dehydration, medications, or other problems may be to blame.
Certain problems that prevent the heart from pumping normally can also cause people to faint. The most common is an arrhythmia, an irregular heartbeat. Another is an abnormally slow heartbeat, called bradycardia. To diagnose these problems, the doctor may ask your mother to wear a portable heart rate monitor for a day or two, or possibly longer. In some cases, people with infrequent fainting spells have a miniature sensor implanted under the skin to detect and record abnormal heart rhythms.