A fast heart beat, or tachycardia, happens when the sinoatrial (SA) node, which is the area of the heart that determines how fast it should beat, sends out a signal that is quicker than usual, according to The American Heart Association. Tachycardia is a heart rate that is more than 100 beats per minute. A normal heart rate is considered to be between 60 and 100 beats per minute.
Tachycardia can be caused by a number of things, including anxiety, drugs, high emotional distress, heavy exercise, fever and fright. In some cases, it can also indicate serious conditions such as heart muscle damage, hemorrhage, increased thyroid activity and anemia.
Tachycardias are classified as narrow complex (supraventricular), which start in the atria, or wide complex, which tend to start in the ventricles. Tachycardia can be caused by a decrease in blood pressure, with the heart increasing the rate of heartbeats in order to compensate. This is known as reflex tachycardia. Increased metabolic needs can also cause tachycardia, usually due to problems such as infection, diarrhea, fever and hyperventilation. Other causes include the body's reaction to stress, known as the fight-or-flight response, the use of stimulants such as cocaine or amphetamine and some endocrine disorders.