Every audible heartbeat is the product of squeezing muscles and pumping blood. These measured contractions are precisely timed to move blood in and out of the heart smoothly and efficiently.
An area of the heart called the sinus (or sinoatrial) node directs the timing of heartbeats using electrical signals. These signals travel through the heart, triggering perfectly synchronized contractions in each of the heart's four chambers. 
When all goes well, this process results in 60 to 100 perfectly timed heartbeats each minute. 
When something interferes with this process, the heart may beat too quickly, too slowly or erratically. This disordered beating is called an arrhythmia. 
Why does it happen? 
Everyone's heart changes pace throughout the day in response to the body's needs. The heart speeds up during physical exercise to provide more blood to working muscles. It slows down during sleep, when the body is at rest. These normal changes help the heart serve the body more effectively. 
Abnormal changes occur when the heart's electrical system malfunctions. This can happen when: 
<ul>
 <li>The heartbeat begins in an area of the heart other than the sinus node. </li>
 <li>The sinus node starts sending irregular electrical signals. </li>
 <li>The signal from the sinus node is blocked or interrupted. </li>
</ul>

Minor arrhythmias, such as the occasional flutter or skipped heartbeat, can occur in response to stress or chemical stimulants, such as caffeine, tobacco, cough and cold medicines, or alcohol.

But when arrhythmias last longer or happen often, they can compromise the heart's function. These more serious arrhythmias often result from heart disease, high blood pressure, damaged heart tissue, a defect in heart structure or other causes. 
Types of arrhythmias 
Arrhythmias may occur in the atria (upper chambers of the heart), ventricles (lower chambers of the heart), the area between the upper and lower chambers (atrioventricular node), or the sinus node. 
They may cause the heart to beat too fast (tachycardia), beat too slow (bradycardia), quiver (fibrillation) or flutter. 
Arrhythmias are named according to where and how they affect the heart. A sinus tachycardia, for example, occurs when the sinus node sends out signals too quickly. Ventricular fibrillation means the ventricles are quivering instead of pumping. 
Signs of trouble 
According to the <a target="_blank" href="[BASEDOMAIN]/healthinfo/bouncelink.aspx?shortcut=aha">American Heart Association</a>, symptoms of arrhythmias may include: 
<ul>
 <li>Fatigue. </li>
 <li>Dizziness. </li>
 <li>Lightheadedness. </li>
 <li>Fainting or near-fainting. </li>
 <li>Rapid heartbeat. </li>
 <li>Shortness of breath. </li>
 <li>Chest pain. </li>
</ul>

When to get help

Arrhythmias range from harmless to life-threatening, but the people who feel them can't necessarily tell the difference. Talk to your doctor about any change in your heartbeat that lasts more than a few seconds or happens frequently. 
Reviewed 8/11/2023

What is an arrhythmia?

Arrhythmias range from harmless to life-threatening.