Ablation Surgery (Catheter Ablation Surgery)
In this procedure, one or more flexible, thin tubes (catheters) are introduced under X-ray guidance into the blood vessels and directed to the heart muscle. A burst of radio frequency energy destroys very small areas of tissue that give rise to abnormal electrical signals.

See External Defibrillator.

Antiarrhythmic Drugs
Medication designed to prevent or treat cardiac arrhythmias.

An irregular heartbeat. This could be a rhythm that's abnormally slow (bradycardia) or a rhythm that's too fast (tachycardia). See also bradycardia and tachycardia.

See Coronary Artery Disease.

Plural for atrium. See Atrium.

Atrial Fibrillation
Extremely rapid, irregular atrial impulses. This rapid rate does not allow the atria to pump blood effectively into the ventricles. It can also cause irregular rapid ventricular beats.

Atrial Flutter
A cardiac arrhythmia in which the atrial contractions are rapid (230-380 per minute), but regular.

Atrioventricular Node (AV node or AV junction)
Electrical signals from the sinoatrial (SA) node travel from the atria through the AV node before moving to the ventricles. The AV node helps keep the upper and lower heart chambers beating in synchrony. When the AV node is blocked, it can result in a slow heartbeat called heart block. An artificial pacemaker can take over an impaired AV node to restore a more normal heart rate.

The heart is divided into four chambers. The upper chambers are called atria, the lower chambers are called ventricles. The atria receive blood from the veins and pump the blood to the ventricles through the tricuspid (right) or mitral (left) valve.

Automatic External Defibrillator (AED)
See External Defibrillator.

A condition in which the heart beats at less than 60 beats per minute. This heart rate may be too slow or irregular to meet the body's demands. (This is different than a physically fit person who may have a heart rate below 60.)

Cardiac Catheterisation
Cardiac catheterisation (also called cardiac cath or coronary angiogram) is a procedure that allows the doctor to "see" how well your heart is functioning. The test involves inserting a long, narrow tube called a catheter into a blood vessel in your arm or leg, and guiding it to your heart with the aid of a special X-ray machine. Contrast dye is injected through the catheter so that X-ray movies of your valves, coronary arteries and heart chambers can be created.

Physician specially trained in the diagnosis and treatment of heart disease.

Cardiomyopathy is a disease of the heart muscle. The heart loses its ability to pump blood and, in some instances, heart rhythm is disturbed, leading to irregular heartbeats, or arrhythmias. Usually, the exact cause of the muscle damage is never found.

Cardiopulmonary Resuscitation
(CPR). The mechanical pushing of the heart (hands pushing on rib cage) and breathing (through the mouth) done in a rhythmic pattern. These actions keep blood and oxygen circulating through the body. CPR is often used as a first emergency response until an external defibrillator can be applied to restart the heart.

An implantable cardioverter defibrillator (ICD) therapy used to treat rapid heart rhythms. Cardioversion consists of shock impulses that may progress from low-energy to high-energy levels, depending on the therapy needed to stop the rapid rhythm.

Cardiovascular Nurse
Works in a hospital area where patients with arrhythmias and other heart problems are monitored.

Cardiovascular Technician
Assists doctors with cardiovascular procedures and surgeries.

Catheter (cath lab; electrophysiology, or EP) lab nurse/technician
Participates in electrophysiology studies and surgeries for pacemakers and implantable cardioverter-defibrillators (ICDs).

Chemotherapy drugs
Certain drugs used in chemotherapy may weaken the heart muscle and result in low ejection fraction and heart failure.

Coronary artery disease (CAD)
One of the most common causes for heart failure. Hardening of the coronary arteries leads to a blockage of blood flow, resulting in a weakening of the heart muscle. Obstructed coronary arteries also cause heart attacks, damaging the affected portion of the heart muscle.

Conduction Pathway
Pathways that conduct electrical impulses to the atria through the atrioventricular (AV) node and around the ventricles, thereby causing the heart to beat and pump blood throughout the body.

An ICD therapy option used to treat ventricular fibrillation. Defibrillation consists of high-energy shock impulses.

See ICD.

Diagnostic Test
This is a test that is ordered by a physician to determine or rule out a condition.

A condition in which the two lower chambers of the heart are not beating together as they do normally. In a normal heart, both sides beat together and are effectively "synchronised."

Echocardiogram (echo)
A type of ultrasound test that uses high-pitched sound waves to produce an image of the heart. An echocardiogram is used to evaluate how well the heart chambers fill with blood and pump blood to the rest of the body with each heartbeat (called the ejection fraction).

A cardiologist who performs cardio-vascular examinations using echocardiograms to produce a picture of a heart and great vessels using high-frequency sound waves.

Ejection fraction (EF)
A measurement of how much blood (what fraction or percentage of blood) the pumping chambers of the heart (the left and right ventricles) are able to pump out, or eject, and supply to the organs (brain, kidneys, liver, etc.) and muscles of your body.

Electrocardiogram (ECG)
A recording of the heart's activity.

A cardiologist with a specialisation in the diagnosis and treatment of arrhythmias. Electrophysiologists are experts in the electrical function of the heart.

Electrophysiology (EP) study
A study used to evaluate the electrical system of the heart.

Exercise ECG
See Stress Test.

External Defibrillation
An electric shock given to the heart through paddles placed on the chest in order to restart the electrical system of the heart. External defibrillation may be done using a manual external defibrillator or an automated external defibrillator (AED).

External Defibrillator (AED)
Portable devices used to electrically stimulate a fibrillating heart. Using an external defibrillator, strong electric shocks are passed between paddles and electrodes placed on a patient's chest.

External Loop Recorder
A device that monitors heart rhythm and rate for up to one month. During this test, the patient wears a device on the wrist or around the waist. When symptoms are experienced, the patient presses a button on the device to make a recording of the heart activity that just occurred.

Heart Attack or Myocardial Infarction
When the heart muscle is damaged because blood is blocked from reaching it, a heart attack occurs. A heart attack is also called a myocardial infarction (MI) because the middle layer of the heart muscle (myocardium) is damaged or is non-functional (infarct).

Heart's Electrical System
The heart has its own electrical system. Special tissues conduct electrical signals that travel along pathways through the heart to stimulate the heart to beat, that is, the contractions of the heart's chambers pump the blood throughout the heart and into the body.

Heart Failure
Heart failure occurs when your heart muscle doesn't pump as much blood as the body needs. "Failure" doesn't mean that the heart has stopped pumping, just that it is failing to pump as effectively as it should. Heart failure is most often caused by a problem with the left ventricle of the heart.

Heart Rhythm Specialist
See Electrophysiologist.

Heart Rhythm Team
A team of doctors, nurses, technician and other healthcare professionals who provide care for your heart condition and other medical conditions.

Heart Valve Disease
Valves within the human heart that open and close automatically to control the flow of blood into, through, and out of the heart. These valves open to ensure that blood flows into the heart chambers as needed, and they close to ensure that blood does not flow back into the heart after it has been pumped out to the lungs and body.

Heavy alcohol use
If alcohol is used excessively over an extended period, it has a toxic effect on the heart muscle.

High blood pressure (hypertension)
Uncontrolled high blood pressure causes the heart to work extra hard to pump blood through the body. A constantly overworked heart ultimately progresses to heart failure.

Holter Monitor
A device that measures and records heart rhythm over 1-3 days. This test may be done when an ECG does not show the arrhythmia and it still is suspected to be the cause of symptoms. Patches with wires are placed on the chest. The wires are connected to a portable monitor that can be attached to a purse or belt.

Implantable (Cardioverter) Defibrillator (ICD)
An ICD is a small device placed inside the body that treats abnormally rapid heart rhythms. It can deliver several types of therapies, including cardioversion, defibrillation, and anti-tachycardia pacing. An ICD is usually implanted in the upper chest or in the abdominal area.

Insertable Loop Recorder
A device that continuously monitors the heart rhythm for up to 14 months. This small device is placed under the skin during a short procedure using a local anaesthetic. When a symptom is experienced, the patient places a hand-held activator over the recorder. Later, a physician analyses the stored information.

A thin insulated wire with electrodes (electrical contacts) located near the tip.

Long-Term Support Pacing Therapy
Sometimes after a shock is delivered, the heart rate may be too slow. If that happens, or if there is any other reason the heart may slow down, the defibrillator sends pacing pulses, like a pacemaker, that raise the heart rate back to normal.

Manual External Defibrillator
Portable devices used to electrically stimulate a fibrillating heart. Using an external defibrillator, strong electric shocks are passed between paddles and electrodes placed on a patient's chest.

Multiple Gated Acquisition Test (MUGA)
A small dose of radioactive material is injected intravenously into the bloodstream. A scanning device then reveals how much blood the heart is able to eject out of both the left and right ventricles.

Myocardial Infarction (MI or heart attack)
After one or several heart attacks, scar tissue prevents the heart from working efficiently, leading to a weakening and dilating of the heart chambers (left and right ventricle) and frequently progressing to heart failure. See Heart Attack.

Myocarditis (inflammation of the heart muscle)
Myocarditis is most often caused by a viral infection, leaving the heart muscle damaged.

Nuclear Scan
For this test, a radioactive substance is injected during exercise. Then a special image is taken of the heart, to see how well blood is flowing through the heart.

A pacemaker system is a two-part electrical system that includes a pulse generator (pacemaker) and one or two leads, or wires, which deliver impulses to the heart. The leads also carry signals back from the heart. By "reading" these signals, the pulse generator is able to monitor the heart's activity and respond appropriately. A pacemaker helps to pace the heart when the natural rate is too slow (bradycardia) to pump enough blood to the body.

The defibrillator may send pacing pulses when the heartbeat is just a little too fast. When several pacing pulses occur rapidly, they usually won't be felt. The patient may feel lightheaded or dizzy because of the rapid heartbeat.

A small computer used at the follow-up clinic to check the pacemaker. The programmer header is often placed over the pacemaker to collect information stored in the pacemaker.

Radionuclide Angiogram (RNA) Test
See Multiple Gated Acquisition Test (MUGA).

Risk Assessment Quiz

A quiz designed to assess a person's risk for Sudden Cardiac Arrest.

Sinoatrial Node (SA node)

A group of cells located in the right atrium that sends out electrical signals which make the heart pump. The SA node is the heart's natural pacemaker. These signals travel from the SA node, through the atrioventricular (AV) node, and then to the rest of the heart. The SA node also responds to the need for a faster heart rate. If a person is exercising or excited, the body will require greater blood circulation. A healthy SA node responds to these changes in the body and increases the heart rate accordingly.

Sinus Node (SA node)

See Sinoatrial Node.

Stress Test

Reveals how well the heart functions during exercise.

Sudden Cardiac Arrest (SCA)

Sudden cardiac arrest is when the heart's lower chambers (ventricles) suddenly develop a rapid, irregular rhythm (ventricular fibrillation) and the quivering ventricles cannot pump blood to the body. Within seconds, the person will not have a pulse and will be unconscious. Without immediate treatment, the person almost always dies. Sudden cardiac arrest is not a heart attack. Heart attack is a problem with the plumbing of the heart; one or more of the arteries delivering blood to the heart is blocked. Oxygen in the blood cannot reach the heart muscle and the heart muscle is damaged.

Sudden Cardiac Death (SCD)

Natural death due to cardiac causes, noted by abrupt loss of consciousness within an hour of the onset of acute symptoms. Preexisting heart disease may or may not have been known to be present, but the time and mode of death are unexpected.

Supraventricular Tachycardia (SVT)

A fast arrhythmia (over 100 beats per minute) that originates an electrical impulse at the top of the heart. There are many types of SVTs, each named for the generator of the abnormal heart rhythm.

Sustained Fast Heart Rhythms (tachycardia)

Tachycardias such as atrial fibrillation (AF) sustained over an extended period may result in low ejection fraction and a damaged heart muscle.


A temporary loss of consciousness due to lack of blood to the main portion of the brain (the cerebrum).


A category of heart rhythm disorders (arrhythmias) characterised by an abnormally rapid or irregular heart rhythm. Known causes of tachyarrhythmias include coronary artery disease, heart attack and heart muscle disease.


See Tachycardia.

Tilt Table Test

This procedure attempts to simulate conditions that may cause arrhythmia. It enables a physician to understand how blood pressure, heart rate and rhythm respond to a change in position from lying down to standing. The patient is positioned on a table, given medication, and the table is tilted by varying degrees. The test typically lasts for a couple of hours.

Valvular Heart Disease

One of the heart's four valves (two aortic, two mitral) may be narrowing (stenosis) or leaking, restricting blood flow to the heart. In certain cases, valvular endocarditis (infection of the heart valves) may cause damage to the valves, impairing blood flow.


One of the two lower chambers of the heart. The right ventricle pumps blood to the lungs. The left ventricle pumps blood to the body's organs.

Ventricular Fibrillation (VF)

A heart rhythm disorder that originates in the ventricles. It is characterised by an abnormally rapid heart rhythm that is also highly unstable and irregular. During VF, electrical signals are moving chaotically through the heart, preventing it from beating properly. This often results in fainting. If left untreated, it may result in cardiac arrest.

Ventricular Tachycardia (VT)

A heart rhythm disorder that originates in the lower chambers. VT is characterised by a rapid heart rhythm during which patients may feel faint or dizzy, or even collapse. During VT, the heart does not pump blood as efficiently as it does during a normal rhythm, and rapid contractions prevent it from filling adequately with blood between beats. VT can be dangerous, life-threatening, if not properly treated.

Last updated: 20 January 2005

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