Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Overview of Abnormal Heart Rhythms


The Manual's Editorial Staff

Reviewed/Revised Jul 2022 | Modified Sep 2022
Get the full details
Topic Resources

Your heart is a muscle that pumps blood through your body. Your heart rate is how fast your heart beats. Your heart should always have a regular, rhythmic beat, like the ticking of a clock.

What is an abnormal heart rhythm?

Abnormal heart rhythms are heartbeats that are:

  • Irregular

  • Too fast (tachycardia)

  • Too slow (bradycardia)

Abnormal heart rhythms are also called arrhythmias.

What controls my heart rhythm?

Your heart rhythm is controlled by:

  • Pacemaker cells in your heart

  • Your brain

  • Hormones, minerals, and other substances in your blood

There are special pacemaker cells in a part of your heart called the SA node (sinoatrial node).

The Conduction System
  • Pacemaker cells send out regular electrical signals to your heart muscle to make it contract

The pacemaker cells have their own natural rhythm of 60 to 100 signals per minute. However, nerves from your brain can send messages to the cells telling them to speed up or slow down.

Your heart's conduction system has tiny strips of tissue sort of like electrical wires.

  • The conduction system carries the pacemaker signals to the rest of your heart

The conduction system includes a gateway called the AV node (atrioventricular node). The AV node controls how signals pass from the upper chambers of your heart (atria) to the lower chambers (ventricles). When the conduction system is working properly, the signals get to each of your heart muscle cells at just the right time so your heart gives a good, strong beat that pumps blood properly.

What causes abnormal heart rhythms?

Your heart rhythm can become abnormal if there's a problem with:

  • Your pacemaker cells

  • Your heart's conducting system

  • Chemicals and drugs in your blood

The most common cause of a heart rhythm problem is a heart disorder, such as:

Coronary artery disease blocks blood flow to parts of your heart. This can damage the pacemaker cells or the conducting system.

Other causes of abnormal heart rhythms include:

  • Medicines

  • Heart abnormalities you were born with

Sometimes doctors can't tell what's causing your abnormal heart rhythm.

What are the symptoms of an abnormal heart rhythm?

Your symptoms depend mainly on whether your heart is:

  • Pumping enough blood

  • Not pumping enough blood

If your heart is pumping enough blood, you may feel normal. Or you may feel like your heart is skipping beats (called palpitations). Some people say strong palpitations may feel like a fish flopping around in their chest.

If your heart is not pumping enough blood, you also may have:

  • Weakness

  • Problems exercising

  • Shortness of breath

  • Feeling light-headed or dizzy

  • Chest pain

  • Fainting

Go to the doctor if you have any of these symptoms.

How can doctors tell if I have an abnormal heart rhythm?

Doctors feel your pulse and do:

An ECG is a quick, painless test that measures your heart’s electrical activity using stickers and cables on your chest, arms, and legs.

If the ECG shows an abnormal rhythm, doctors usually do other tests depending on your symptoms, including:

If the ECG does not show an abnormality, it could be because your heart rhythm was not abnormal while you were having the test. Doctors then may have you:

If doctors think you have a dangerous heart problem, they'll admit you to the hospital. You'll be in a unit where your heart rate and rhythm can be recorded and seen by the nurses and doctors.

If doctors need more information about your abnormal heart rhythm, they may do:

Electrophysiologic testing is like cardiac catheterization Cardiac Catheterization Cardiac catheterization (also called cardiac cath) is a heart procedure done in a hospital. The doctor puts a thin plastic tube (catheter) through an artery and into your heart. Doctors get... read more Cardiac Catheterization . Doctors insert a thin flexible tube (catheter) into a large blood vessel (for example, one in your leg) and thread it up into your heart. The catheter has electrodes on its tip that record your heart's electrical activity from the inside. The catheter can also stimulate your heart electrically to see how it responds.

How do doctors treat abnormal heart rhythms?

Some abnormal heart rhythms are harmless and don’t need treatment.

Sometimes, lifestyle changes help, such as:

  • Changing or stopping one of your medicines

  • Not drinking alcohol or caffeine

  • Not smoking

  • Not doing heavy exercise (if an abnormal heart rhythm happens during exercise)

Different abnormal rhythms require different treatment. Doctors may use:

  • Medicines

  • An artificial pacemaker (a small electrical device that doctors put in your chest or belly to signal your heart when to beat)

  • An electrical shock to restore normal heart rhythm (called cardioversion, defibrillation, or electroversion)

  • A treatment called ablation to destroy the abnormal heart tissue

Artificial pacemakers sometimes include a defibrillator so the same device can trigger a normal heart beat or stop an abnormal rhythm with a shock. This combination device is called an ICD (implantable cardioverter-defibrillator).

Doctors do ablation if they find that one small bit of heart tissue is causing the abnormal rhythm. Getting rid of the tissue often gets rid of the rhythm problem. Often they do ablation during electrophysiologic testing. They use a catheter to deliver a high-frequency electrical current that destroys a small area of the heart.

You may need to stop driving for a while until doctors know whether the treatment is working.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Cafcit, NoDoz, Stay Awake, Vivarin
quiz link

Test your knowledge

Take a Quiz!