The most common cause of a fast rapid heartbeat is sinus tachycardia — defined as a regular heartbeat at a rate greater than 100 beats per minute.
Sinus tachycardia is a normal response to exercise, feeling anxious, fever, dehydration, and many other circumstances. The heart is actually doing what it is supposed to do.
Other causes of a fast regular heart beat include certain types of arrhythmias. With no other symptoms but the palpitations, these need to be treated but are rarely dangerous.
If the palpitations recur, contact your doctor.
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