An arrhythmia is a disorder of the heart that affects the rate or rhythm at which the heart beats. An arrhythmia occurs when electrical impulses, which direct and regulate heartbeats, don’t function properly. This causes the heart to beat:

  • too fast (tachycardia)
  • too slow (bradycardia)
  • too early (premature contraction)
  • too erratically (fibrillation)

Nearly everyone will experience an abnormal heart rhythm at least once. It may feel like your heart is racing or fluttering. Arrhythmias are common and usually harmless, but some are problematic. When an arrhythmia interferes with blood flow to your body, it can damage your brain, lungs, and other vital organs. If not treated, these arrhythmias may be life-threatening.

Your heart is divided into four chambers. Each half of your heart consists of an upper chamber (the atrium) and a lower chamber (the ventricle). The two halves create two pumps, one on either side of the heart.

In a properly beating heart, electrical impulses follow precise pathways through the heart to each pump. These signals coordinate the activity of the heart muscle so that blood pumps in and out of the heart. Any interruption in these pathways or impulses can cause the heart to beat abnormally.

The heartbeat

Blood enters the heart and arrives first in the atria. Then, a single heartbeat involves several steps:

  • The sinus node (a group of cells in the right atrium) sends an electrical impulse to both the right and left atria, telling them to contract.
  • This contraction allows the ventricles to fill with blood.
  • While the ventricles fill, the electrical impulse travels to the center of your heart to the atrioventricular node (a group of cells between the atria and the ventricles).
  • The impulse exits the node and travels to the blood-filled ventricles, telling them to contract.
  • This contraction pushes the blood out of the heart and into your body for circulation.

That is one heartbeat. Then the process starts all over again. Under normal conditions, the left and right sides of the heart beat one after the other. This keeps the blood flow moving in one direction in a continuous pumping fashion.

A normal heart will repeat this process about 100,000 times each day. That’s 60 to 100 beats per minute for the average healthy person while at rest.

Arrhythmias are named and categorized based on three points:

  • rate (whether it’s too slow or too fast)
  • origin (whether it’s in the ventricles or the atria)
  • regularity


Bradycardia is a slow heartbeat. It’s defined as a resting heart rate of fewer than 60 beats per minute. Not all bradycardias are a problem. Athletes and people who are physically fit often have bradycardias. Their resting heart rates may be fewer than 60 beats per minute because their hearts are more efficient and can pump adequate blood with fewer beats. However, a slow heart rate might mean your heart doesn’t beat frequently enough to ensure adequate blood flow throughout your body.

Types of bradycardia include:

Sick sinus: The sinus node is responsible for setting the pace of your heart. If it isn’t sending electrical impulses properly, your heart may pump too slowly or irregularly. Scarring near the sinus node from heart disease or a heart attack may also slow down or block the electrical impulses as they try to travel through the heart.

Conduction block: If your heart’s electrical pathways are blocked, the chambers of the heart may contract slowly or not at all. A block can happen anywhere along the heart’s electrical pathways—between the sinus node and atrioventricular (AV) node, or between the AV node and the ventricles. There may be no signs of these blocks other than skipped or slowed heartbeats.


Tachycardia is a fast heartbeat. It’s defined as a resting heart rate of more than 100 beats per minute. The two most common types of tachycardia are supraventricular tachycardia and ventricular tachycardia.

Supraventricular tachycardia: Supraventricular tachycardia (SVT) is any arrhythmia that begins above the ventricle. SVTs are usually identified by a burst of rapid heartbeats that can be chronic or begin and end suddenly. These bursts can last a few seconds or several hours and may cause your heart to beat more than 160 times per minute. The most common SVTs include atrial fibrillation and atrial flutter.

Atrial fibrillation: If you have atrial fibrillation (AF), your atrium beats very rapidly (as fast as 240 to 350 beats per minute). The atria move so rapidly that they aren’t able to contract completely. Instead, they quiver, or fibrillate. This can cause discomfort, but not a rapid pulse. However, some of these atrial beats can transfer to the ventricles and may cause a high pulse rate.

AF primarily affects older people. Your risk of developing this arrhythmia increases past age 60, mostly due to the wear an older heart experiences. The chances of developing AF are also high if you have or have had high blood pressure or other heart problems. AF can be dangerous. If left untreated, it can lead to more serious conditions, such as stroke.

Atrial flutter: The heartbeats in atrial flutter are more rhythmic and constant than the heartbeats in atrial fibrillation. Still, atrial flutter can come and go in sudden bursts. It can be life-threatening. This type of arrhythmia occurs most often in people with heart disease. It also often shows up in the first weeks after heart surgery.

Ventricular tachycardia: Ventricular tachycardia (VT) is an arrhythmia that begins in the ventricles of the heart. Most VT occurs in people who have had heart disease or heart-related problems, such as coronary artery disease or heart attack. VT is often caused by an electrical impulse traveling around a scarred part of the heart’s muscle. It can cause the ventricles to contract more than 200 times per minute. If left untreated, VT may increase your risk of developing more serious ventricular arrhythmias, such as ventricular fibrillation (VF).

Ventricular fibrillation: VF may have signs such as sudden, rapid, irregular, and chaotic heartbeats in the ventricle. These erratic electrical impulses, sometimes triggered by a heart attack, cause your heart’s ventricles to quiver (fibrillate). When you have this kind of arrhythmia, your ventricles can’t pump blood into your body, and your heart rate drops quickly. This makes your blood pressure fall and diminishes the blood supply to your body and organs. VF is the number one cause of sudden cardiac arrest.

Premature heartbeats

Premature heartbeats may result in the feeling that your heart has skipped a beat. In reality, your normal heart rhythm has been interrupted by a too-soon beat, and you’re experiencing an extra beat between two normal heartbeats.

There are many types of heart arrhythmias. Most are harmless, and nearly everyone has an arrhythmia at one time or another. Frequently, they go unnoticed. It’s also normal to have an increased heart rate during exercise, when your heart is working hard to provide your tissues with oxygen-rich blood so you don’t fatigue too quickly. Athletes and people who are physically fit may have slow heart rates because their hearts work very efficiently and don’t require as many beats as others who exercise less often.

Some arrhythmias are not harmless, though. Your outlook depends on the type and severity of your arrhythmia. If you think you have an arrhythmia, you should see your doctor. Even the most serious arrhythmias can often be treated successfully. Most people with arrhythmia can live a normal life.