Rather than just listing the causes, here is my approach to investigating a fast heartbeat.

First, I would like to know if you have any other symptoms, especially chest pain, shortness of breath, dizziness, and/or feeling faint. Any of these could suggest an abnormal heart rhythm. If you have any of these and a fast heartbeat, you should call your doctor right away.

Ideally, I would want you to check your pulse at the time you feel your heart rate is high. Sometimes, it can feel like your heart is racing when actually it is in the normal range, which is less than 100 beats per minute. Doctors refer to a heart rate of 100 or higher as tachycardia.

As long as you feel perfectly fine, tachycardia rarely has a serious cause. But having other symptoms with tachycardia requires a medical consultation.

While checking your pulse, I would want to determine if the heartbeat is regular (steady, like clockwork) or irregular (jumping around or skipping beats).

Causes of regular rapid heartbeat (regular tachycardia) other than exercising or anxiety include:

• Fever
• Dehydration
• An overactive thyroid gland (hyperthyroidism)
• A heart rhythm abnormality, such as atrial tachycardia, atrial flutter and ventricular tachycardia. However, these would almost always cause additional symptoms, not just a fast heart rate.

The most common cause of a very irregular fast heartbeat is atrial fibrillation.

I suggest that you call your doctor to discuss your symptoms. If he or she has any concern, the next step would be a routine EKG. Additional testing might include wearing a heart monitor, called a Holter or event monitor. This device records your heart rate and rhythm for 24 hours or longer.