Tachycardia means a fast heart rate. The normal adult heart rate, or pulse, ranges from 60 to 100 beats per minute. A heart rate that stays above 100 beats per minute is called tachycardia.

A fast heart rate can occur naturally. For example, your heart rate may increase when you are exercising, but it returns to normal when you rest. A fast heart rate can also be caused by serious, life-threatening heart problems.
How does it occur?

Your heart rate normally increases in several situations, such as when you:

• exercise
• have a fever
• are anxious or excited.

Hyperthyroidism (too much thyroid hormone in your body) can cause a fast heartbeat. Problems with the heart that can also cause tachycardia are:

• Paroxysmal atrial tachycardia (PAT) and supraventricular tachycardia (SVT): These forms of tachycardia are disturbances in the natural electrical impulse that causes your heart to pump. If you have PAT or SVT, it does not necessarily mean that you have a serious heart problem.
• Atrial fibrillation: This is an abnormal rhythm pattern where the right and left atria (upper heart chambers) are contracting irregularly and making the heart beat faster.
• Ventricular tachycardia: This is a less common, but more dangerous kind of tachycardia. The heart beats in a regular rhythm but very fast. This abnormality is caused by heart disease. In a few cases it can be due to medication you are taking, such as digitalis or quinidine. The problem starts in your ventricles (lower heart chambers). The most serious aspect of ventricular tachycardia is that it can become ventricular fibrillation.
• Ventricular fibrillation: This is the most serious type of tachycardia. Your heart beats in an irregular rhythm and very fast. Your ventricles contract (squeeze) chaotically, which prevents the heart from pumping. When this happens, blood circulation stops. Sometimes the episodes are brief and suddenly go away. Most often, however, ventricular fibrillation requires immediate medical treatment to prevent brain damage or death.
• Mitral valve prolapse: This mild deformity of one of the valves in your heart can cause a fast heart rate.

The main symptom is the sensation of a fast heartbeat. Other symptoms of tachycardia that may require medical treatment are:

• lightheadedness or fainting
• nausea
• cold sweat
• shortness of breath
• chest pain.

These symptoms may be caused by any type of tachycardia, mild to severe. Contact your health care provider if you are having any of these other symptoms in addition to the fast heartbeat.
How is it diagnosed?

Your health care provider will ask about your medical history, including your symptoms. He or she will examine your heart and lungs. You may have blood tests to check for underlying metabolic diseases, such as thyroid disease. You will have a chest x-ray and electrocardiogram (ECG). An ECG measures the electrical activity of your heart. Usually a rhythm strip is done; this is a continuous ECG for 1 to 2 minutes to look for heart rhythm abnormalities.

Your health care provider may want you to wear a Holter monitor for 24 to 72 hours. The Holter monitor is a portable ECG used to detect heart rhythm disturbances. If your tachycardia seems related to exercise, you may need to have an ECG while exercising on a treadmill.
How is it treated?

The treatment depends on which type of tachycardia you have. Treatment may range from exercise conditioning to control of anxiety symptoms. It may include medication.

Electrical shock may be necessary with atrial fibrillation, and especially with ventricular tachycardia and ventricular fibrillation. Implanted electroshock units are now being used for some people with a high risk of having ventricular fibrillation. In cases of life-threatening heart rhythm problems, these units could provide instant, life-saving electrical shock before medical help arrives.
What can I do to help prevent tachycardia?

The best prevention is to have a heart-healthy lifestyle:

• Maintain a healthy weight.
• Eat a healthy diet.
• Get regular exercise, as recommended by your health care provider.
• Don't smoke.
• Seldom use other stimulants, for example, caffeine.
• Have regular medical check-ups after age 40.