Accessory Pathway An abnormal muscular connection beetween the upper and lower chambers of the heart. Patients with accessory pathways may develop supraventricular tachycardias. Some patient with accessory pathways also have the Wolff-Parkinson-White syndrome.

Arrhythmia An irregular heart rhythm, or an abnormality in the timing or pattern of the heartbeat, causing the heart to beat too rapidly, too slowly, or irregularly.

Arrhythmogenic Right Ventricular Dysplasia (ARVD) A familial disorder that may cause ventricular arrhythmias.

Atrial Fibrillation Rapid, uncoordinated firing of electrical impulses from multiple sites in the upper chambers, which causes ineffective contractions. A type of supraventricular tachycardia.

Atrial Flutter A single "short circuit" in the atria that causes the atria to beat at about 300 beats per minute while the lower chambers of the heart (the ventricles) beat at a slower rate (often 75 or 150 beats per minute). A type of supraventricular tachycardia.

Atrial Tachycardia A sustained, irregular heart rhythm that occurs in the upper chamber of the heart and causes it to beat too rapidly.

Atrium, Atria (plural) The two upper chambers of the heart, which receive blood from the body.

AV Nodal Re-entrant Tachycardia (AVNRT) An abrupt, rapid heartbeat that occurs when electrical impulses mistakenly enter an extra pathway in or near the AV node. A type of paroxysmal supraventricular tachycardia.

AV Node The normal electrical connectoin between the atria and the ventricles where electrical impulses are delayed for a fraction of a second to allow the lower chambers to fill completely with blood.

Bradycardia A slow heart rate (less than 60 beats per minute).

Cardioversion A procedure used to shock your heart back into rhythm. Most likely used with patients who have either atrial fibrillation or atrial flutter.

Catheter Ablation A procedure used to destroy (ablate) areas of the heart that are causing arrhythmias. In a radiofrequency (RF) ablation, electrophysiologists pinpoint the area and then use radio wave energy to "cauterize" the tiny part of the heart muscle causing the heart rhythm abnormality.

Echocardiogram A non-invasive test in which sound waves are used to produce an image of the heart.

Electrocardiogram (ECG) A simple test that traces the electrical activity of your heart. Also known as an EKG.

Electrophysiology The study of electrical activity in the heart.

Electrophysiologist A cardiologist (heart doctor) who specializes in the electrical system of the heart.

Electrophysiology Study A test that allows the electrophysiologist to examine the electrical activity inside your heart and evaluate any abnormalities.

Event Monitor A wearable monitor that records the heart rhythm only when activated. Typically used for one month, during which patients are instructed to trigger the device if symptoms occur.

Exercise Stress Test A test that determines irregular heart rhythms while exercising. Also known as a treadmill test.

Heart Block A complete or partial interruption of the electrical impulses on their way to the ventricles that results in a slow, unreliable heartbeat. A type of bradycardia.

Holter Monitor A wearable monitor used to obtain a continuous ECG recording, usually for 24-48 hours, useful for detecting abnormalities that may not occur during a resting ECG.

Implantable Cardiac Defibrillator (ICD) Device commonly used to treat patients who have experienced a potentially dangerous ventricular arrhythmia. These devices continuously monitor the heartbeat and automatically deliver a small electrical shock to the heart if a sustained rapid heart rhythm occurs.

Implantable Holter Monitor Device that is inserted under the skin (similar to a pacemaker) and functions like an event monitor to determine the cause of infrequent fainting.

Pacemaker A device used primarily to correct some types of bradycardia, or slow heart rhythms. The pacemaker is implanted in the body, usually below the collarbone, where it monitors the heart rhythm and supplies electrical triggers to the heart if it is beating too slowly.

Paroxysmal Supraventricular Tachycardia (PSVT) A "short circuit" arrhythmia that causes the heart to beat too rapidly. PSVT may be misdiagnosed as a panic attack.

Sick Sinus Syndrome Disorder in which the sinus node (the heart's own pacemaker) fails and does not trigger enough heartbeats. A type of bradycardia.

Signal-Averaged Electrocardiogram (SAECG) A type of ECG recording that can determine if scarred tissue, which may predispose one to a heart arrhythmia, is present in your heart.

Sinus Node The sinus node, a group of specialized cells in the right atrium, is the place where the electrical impulse in the heart normally begins. It functions as the heart's pacemaker, setting the pace for the heartbeat.

Supraventricular Tachycardia A series of rapid heartbeats arising from the upper chambers of the heart that can cause the heart to beat very rapidly or erratically and may lead to inadequate blood supplies to the body.

Tilt Table Test Test used to diagnose an abnormality of blood pressure regulation which may cause lightheadedness or a passing out spell.

Ventricles The two major pumping chambers of the heart.

Ventricular Tachycardia A series of rapid heartbeats that originate in the lower chamber of the heart (the ventricles) which may cause the heart to beat inefficiently.

Wolff-Parkinson-White Syndrome A specific type of heart rhythm abnormality. Patients with the WPW syndrome have an accessory pathway connecting the upper and lower chamber of the heart. These patients may develop a rapid heartbeat caused by a "short circuit" heart arrhythmia. WPW syndrome also may cause dangerous heart arrhythmias.