At one time or another, most people have felt “faint” from the sight of blood or an intense emotion such as fright. Blood vessels in the trunk of the body have an immense capacity to hold blood—nearly the entire blood volume of the body, in fact. A strong shock or fright might cause these vessels to fill with so much blood that pressure drops in other blood vessels, particularly those supplying the brain, causing lightheadedness or even a brief loss of consciousness.
So too, anyone who is made to stand absolutely still for a prolonged time, such as soldiers at attention, may faint. The reason is that blood pools in the legs, causing too little blood to be pumped to the brain.
Such episodes of fainting, which doctors call syncope (SIN-kuh-PEE), usually occur for clear reasons and may be regarded as normal. When fainting doesn’t have an obvious cause, however, it could be a warning sign of a serious, even life-threatening heart disorder. The problems include:
- Bradycardia. This condition, which means slow heartbeat, can reduce the flow of blood to the brain.
- Heart attack. A blockage in one or more arteries within the heart may prevent enough blood from flowing to the brain.
- Heart valve disease. Any disorder within the heart’s valves can prevent the synchronous flow of blood from one chamber to another—and to the brain and other organs.
- Iron-deficiency anemia. While not a heart disease in itself, a shortage of iron in the blood can reduce the number of red blood cells that carry oxygen to the brain.
- Low blood pressure. A reduction in the pressure needed to push the blood through the body’s long system of arteries and veins can reduce the volume of blood that reaches the brain.
- Stroke. A blockage in an artery in the neck or head can cut off the supply of blood to a portion of the brain.
- Medication. Some medications, notably certain drugs used to lower blood pressure, may cause light-headedness, a feeling of faintness and even fainting spells.
If you’ve experienced fainting spells for no apparent reason, be sure to see your doctor. Serious heart problems that cause fainting can almost always be treated successfully.