Causes

Tachycardia is caused by something that disrupts the normal electrical impulses that control the rate of your heart's pumping action. Many things can cause or contribute to a fast heart rate. These include:

• Anemia
• Drinking too many caffeinated beverages
• Drinking too much alcohol
• Exercise
• Fever
• High or low blood pressure
• Imbalance of electrolytes, mineral-related substances necessary for conducting electrical impulses
• Medication side effects
• Overactive thyroid (hyperthyroidism)
• Smoking
• Sudden stress, such as fright
• Use of stimulant drugs, such as cocaine or methamphetamine

In some cases, the exact cause of tachycardia can't be determined.

The heart's electrical system

To understand the causes of heart rate or rhythm problems such as tachycardia, it helps to understand how the heart's electrical system works.

Your heart is made up of four chambers — two upper chambers (atria) and two lower chambers (ventricles). Your heartbeat is normally controlled by a natural pacemaker called the sinus node, which is located in the right atrium. The sinus node produces electrical impulses that normally start each heartbeat.

From the sinus node, electrical impulses travel across the atria, causing the atrial muscles to contract and pump blood into the lower chambers of the heart (ventricles).

The electrical impulses then arrive at a cluster of cells called the atrioventricular (AV) node — usually the only pathway for signals to travel from the atria to the ventricles.

The AV node slows down the electrical signal before sending it to the ventricles. This slight delay allows the ventricles to fill with blood. When electrical impulses reach the muscles of the ventricles, they contract, causing them to pump blood either to the lungs or to the rest of the body.

When anything disrupts this complex system, it can cause the heart to beat too fast (tachycardia), too slow (bradycardia) or with an irregular rhythm.