Arrhythmia: any deviation from the normal rhythm of the heart. Arrhythmias result from a disturbance of the generation or the conduction of electrical impulses and may be intermittent or continuous. (OxfordMed, 51) Very common. Millions of people will experience an abnormal heart rhythm some time during their lives. Most are not serious. (HRS, Heart Rhythm Foundation Glossary) ‘Supraventricular arrhythmia’ is an arrhythmia that begins in the “atria” and ‘ventricular arrhythmia’ is an arrhythmia that begins in the “ventricles.” (Cleveland Clinic, Diseases & Conditions)

Bradycardia: slow heart rhythms that may be caused by disease in the heart’s ‘conduction system,’ such as the “sinoatrial node” “atrioventricular node,”  or “HIS-Purkinje network.” (Cleveland Clinic, Diseases & Conditions) Slowing of the heart rate to less than 50 beats per minute. Often found in healthy individuals, especially athletes, but it is also seen in some patients with reduced “thyroid” activity. (OxfordMed) Describes a heartbeat that is too slow. A normal heart contracts about 100,000 times each day, at a rate of 60 to 100 times a minute. The weak pace may mean the heart doesn't beat often enough to ensure blood flow. Slow heart rates can be the result of certain medications, congenital heart disease, or the degenerative processes of aging. (HRS, Heart Rhythm Disorders Facts) Also referred to as ‘bradyarrhythmia’ and ‘brady.’

Fibrillation: chaotic electrical and mechanical activity of a heart chamber, which results in loss of synchronous contraction. The affected part of the heart then ceases to pump blood. (OxfordMed) Describes a heartbeat that is chaotic, or irregular, and may seem to skip beats or beat out of rhythm. This occurs when a chamber of the heart goes into spasm and fails to pump. There are two types of fibrillation: atrial fibrillation and ventricular fibrillation. (HRS, Heart Rhythm Disorders Facts)

Atrial Fibrillation: an irregular and rapid heartbeat in the atria. (HRM, Heart Rhythm Disorders Facts) Many impulses begin and spread through the atria, competing for a chance to travel through the AV node. The resulting rhythm is disorganized, rapid and irregular. Because the impulses are traveling through the atria in a disorderly fashion, there is a loss of coordinated atria contraction. (Cleveland Clinic, Diseases & Conditions) Caused by a problem in the conduction of electrical impulses in the atria. Electrical signals that coordinate the muscle of the atria become rapid and disorganized; resulting in an irregular heartbeat, often greater than 300 beats per minute. Signs and symptoms vary, and may include a sudden flutter of the heart, anxiety, shortness of breath, weakness and difficulty exercising, chest pain, sweating, dizziness or fainting. (HRS, Atrial Fibrillation Facts) Most common sustained heart rhythm disorder. Increases the risk of heart disease and stroke. More than two million people in the United States have atrial fibrillation and 160,000 new cases are diagnosed each year. (HRS, Heart Rhythm Disorders Facts) In 'paroxysmal A-Fib' episodes end spontaneously. This type of atrial fibrillation usually comes on suddenly, and its symptoms can range from mild to severe. The irregular heart rhythm may last for a few seconds, minutes, hours or longer before the heart resumes a normal rhythm on its own. 'Permanent A-Fib' is when normal rhythm cannot be restored.  In 'persistent A-Fib' the irregular heart rhythm continues indefinitely unless it is treated. (HRS, Atrial Fibrillation Facts) Also referred to as 'A-Fib.'

Ventricular Fibrillation: an erratic, disorganized firing of impulses from the ventricles. The ventricles quiver and cannot generate an effective contraction, which results in a lack of blood being delivered to the body. This is a medical emergency that must be treated with ‘cardiopulmonary resuscitation’ and ‘defibrillation’ as soon as possible. (Cleveland Clinic, Diseases & Conditions) Abrupt and happens without any warning, and halts all heart functioning. The (resultant) lack of oxygen throughout the body, and especially to the brain, is deadly. (HRS, Heart Rhythm Foundation Glossary) When ventricular fibrillation occurs the ventricles stop beating. It is most commonly the result of “myocardial infarction.” (Oxford Med) Also referred to as ‘V-Fib.’

Preexcitation Arrhythmia: impulses travel to the ventricle earlier than what you would expect them to if they traveled down the normal pathway through the “AC node.” (Cleveland Clinic, Diseases & Conditions) An electrocardiographic finding characterized by a premature activation of the whole or some part of the ventricle. (NCIt)

Premature Heartbeat: occurs when the heart's regular rhythm is interrupted by early or premature beats. It may feel as if the heart has skipped a beat. Usually it is not serious. (HRS, Heart Rhythm Disorders Facts)

Premature Atrial Contraction (PAC): early, extra heartbeats that originate in the atria. (Cleveland Clinic, Diseases & Conditions) Also referred to as ‘premature atrial beats.’

Premature Ventricular Contraction (PVC): early, extra heartbeats that originate in the ventricles. The pattern is a normal beat, an extra beat (the ‘PVC’), a slight pause, then a stronger-than-normal beat. This pattern may occur randomly or at definite intervals. Most of the time, PVCs don’t cause any symptoms or require treatment. Common and can be related to stress, too much caffeine, nicotine, or exercise. (Cleveland Clinic, Diseases & Conditions) Also referred to as ‘premature ventricular beats.’

Tachycardia: a increase in the heart rate above normal. (OxfordMed) Rapid beating of the heart, usually defined as greater than 100 beats per minute. (NCI1) A healthy adult heart normally beats 60 to 100 times a minute when a person is at rest. If you have tachycardia, the rate in the upper chambers or lower chambers of the heart, or both, is increased significantly. (Mayo, 00929) A too-rapid heartbeat. It is the number one cause of “sudden cardiac arrest.” (HRS, Heart Rhythm Disorders Facts) Can be dangerous because the racing interferes with the heart’s ability to contract properly. (HRS, Heart Rhythm Foundation Glossary) Also referred to as ‘tachy.’

Sinus Tachycardia: a harmless rhythm. A normal increase in heart rate that happens with fever, excitement, and exercise. It does not require treatment except in rare cases. (HRS, Heart Rhythm Foundation Glossary) A disorder characterized by an "electrocardiograph" finding of abnormally rapid heart rate with its origin in the 'sinus node.' Thresholds for different age, gender, and patient populations exist. (NCIt)

Supraventricular Tachycardia (SVT): a rapid heart beat that is usually due to a ‘re-entry’ (pathway) between the atria and ventricles in the context of an “accessory pathway.” (OxfordMed) A disorder characterized by a dysrhythmia with a heart rate greater than 100 beats per minute that originates above the ventricles. (NCIt) Also referred to as ‘atrial tachycardia.’

Accessory Pathway Tachycardia: a fast heart rhythm caused by an extra, abnormal electrical pathway or connection between the atria and ventricles. The impulses travel through the extra pathways as well as the usual route. This allows the impulses to travel around the heart very quickly, causing the heart to beat unusually fast. (Cleveland Clinic, Diseases & Conditions)

Wolff-Parkinson-White Syndrome (WPW): "congenital" abnormality of heart conduction caused by the presence of an 'accessory' pathway of conduction between the atria and ventricles. (OxfordMed) Episodes of fast heart rate caused by an extra electrical pathway. The fast heart rate often occurs because the electrical impulses go down one pathway from the atria to the ventricles and then return to the atria through the other pathway. (MayoWPW) When you have WPW, along with your normal conduction pathway, you have extra pathways called 'accessory pathways.' They look like normal heart muscle, but they may conduct impulses faster than normal and/or conduct impulses in both directions. The impulses travel through the extra pathway as well as the normal "HIS Purkinje network." The impulses can travel around the heart very quickly, in a circular pattern, causing the heart to beat unusually fast. This is called re-entry tachycardia. Re-entry arrhythmias occur in about 50 percent of people with WPW; some may have atrial fibrillation. The greatest concern for people with WPW is the possibility of having atrial fibrillation with a fast ventricular response that worsens to ventricular fibrillation, a life-threatening arrhythmia. (Cleveland Clinic, Diseases & Conditions)

Atrial Flutter (AFL): an atrial arrhythmia caused by one or more rapid circuits (pathways) in the atrium. Usually more organized and regular than atrial fibrillation. (Cleveland Clinic, Diseases & Conditions) An electrical wave (that) circulates very rapidly in the upper chambers of the heart. (HRS, Atrial Fibrillation Facts) Instead of many disorganized signals, AFL is caused by a single electrical wave that circulates very rapidly in the atrium, about 300 times a minute, leading to a very fast, steady heartbeat. (HRS, Heart Rhythm Foundation Glossary)

AV Nodal Re-entry Tachycardia (AVNRT): a fast heart rhythm caused by the presence of more than one pathway through the “atrioventricular node.” (Cleveland Clinic, Diseases & Conditions) A rapid heart rate due to a self-sustaining circulation of electrical impulses from the atria to the ventricles and back again. This re-entry circuit requires the presence of an abnormal accessory pathway of electrical conduction in addition to the atrioventricular node. (OxfordMed)

Paroxysmal Supraventricular Tachycardia (PSVT): a rapid but regular heart rhythm that comes from the atria. This type of arrhythmia begins and ends suddenly. (Cleveland Clinic, Diseases & Conditions) An ‘electrocardiographic’ finding of episodic supraventricular tachycardia with abrupt onset and termination. (NCIt)

Ventricular Tachycardia (VT): a dangerously fast beating of the heart stemming from an abnormal focus of electrical activity in the ventricles. The electricity does not pass through the heart along the usual channels and as a result the contraction of the heart muscle is often not as efficient as normal, which can result in a sudden drop in blood pressure or even cardiac arrest. (OxfordMed) The rapid rhythm keeps the heart from adequately filling with blood, and less blood is able to pump through the body. (Cleveland Clinic, Diseases & Conditions) At times, ventricular tachycardia can change without warning into ventricular fibrillation. (HRS, Heart Rhythm Disorders Facts) Because it can lead to ventricular fibrillation, it is considered a serious condition that warrants aggressive monitoring and treatment. (HRS, Heart Rhythm Foundation Glossary) Also referred to as ‘V-tach.’ 

Long-QT Syndrome: 'Q' and 'T' are letters on the "electrocardiogram," the tracing of the electrical impulses of our beating hearts, and long QT means that a certain part takes a bit too long. (Batiza, 19) When the “QT interval” is longer than normal, it increases the risk for ‘torsade de pointes,’ a life-threatening form of ventricular tachycardia. (Cleveland Clinic, Diseases & Conditions)

Atherosclerosis: build-up of fatty material and calcium deposition in the arterial wall resulting in partial or complete “occlusion” of the arterial “lumen.” (NCIt) Hardening of the arteries, also called atherosclerosis, is a common disorder. It occurs when fat, cholesterol, and other substances build up in the walls of arteries and form hard structures called “plaques.” Over time, these plaques can block the arteries and cause problems throughout the body. Clots may form in these narrowed arteries and block blood flow. Pieces of plaque can also break off and move to smaller blood vessels, blocking them. The blockage starves tissues of blood and oxygen, which can result in damage or tissue death. This is a common cause of heart attack and stroke. (PubMedHealth2) Also referred to as ‘hardening of the arteries.’

Cardiac Arrest: cessation of cardiac activity in an individual who becomes unresponsive, without normal breathing and no signs of circulation. (NCIt)  The cessation of effective pumping action of the heart. This may be because the heart stops beating altogether because there is a normal electrical activity without mechanical pumping activity, or because there is rapid, chaotic, ineffective electrical and mechanical activity of the heart. There is abrupt loss of consciousness, absence of the pulse, and breathing stops. Unless treated promptly, irreversible brain damage and death follow within minutes. (OxfordMed)

Sudden Cardiac Arrest (SCA): (condition where) the heart abruptly and unexpectedly ceases to function. The most common cause is ventricular fibrillation. (HRS, Heart Rhythm Foundation Glossary) Within seconds, an individual loses consciousness and, without immediate emergency treatment, will die within minutes. SCA is a leading cause of death in the United States, claiming more than 250,000 lives per year. Cardiovascular disease is the leading cause of death in the U.S. and most deaths from cardiovascular disease are attributable to SCA. (HRS, Heart Rhythm Disorders Facts)

Cardiomyopathy: any chronic disorder affecting the muscle of the heart. (OxfordMed) Occurs when the heart muscle is too weak to effectively pump blood through the body. (HRS, Heart Rhythm Foundation Glossary) A weakening of the heart muscle or another problem with the heart muscle. It often occurs when the heart cannot pump as well as it should, or with other heart function problems. (PubMedHealth2) Failure of the heart to pump a sufficient amount of blood to meet the needs of the body tissues. A weakness of the heart muscle that leads to a buildup of fluid in body tissues. (NCIt) Also referred to as ‘heart failure’ and ‘congestive heart failure.’

Myocardial Infarction: death of a segment of heart muscle, which follows interruption of its blood supply. (OxfordMed) Most heart attacks are caused by a "blood clot" that blocks one of the coronary arteries. The coronary arteries bring blood and oxygen to the heart. If the blood flow is blocked, the heart is starved of oxygen and heart cells die. Occurs when blood flow to a part of your heart is blocked for a long enough time that part of the heart muscle is damaged or dies. A hard substance called plaque can build up in the walls of your coronary arteries (and block them). (PubMedHealth2) Also referred to as a ‘heart attack.’

Congenital Heart Disease: a heart disease that is present at birth. (NCIt) A problem with the heart's structure and function that is present at birth. The most common type of birth defect. Congenital heart disease causes more deaths in the first year of life than any other birth defects. (PubMedHealth2)

Coronary Heart Disease: a narrowing of the small blood vessels that supply blood and oxygen to the heart. (PubMedHealth2) A narrowing or blockage of the “coronary arteries.” Coronary artery disease is usually caused by atherosclerosis. The disease may cause chest pain, shortness of breath during exercise, and heart attacks. The risk of coronary artery disease is increased by having a family history of coronary artery disease before age 50, older age, smoking tobacco, high blood pressure, high cholesterol, diabetes, lack of exercise, and obesity. (NCIt) 'Coronary artery spasm' is a temporary, sudden narrowing of one of the coronary arteries (the arteries that supply blood to the heart). The spasm slows or stops blood flow through the artery and starves part of the heart of oxygen-rich blood. (PubMedHealth2) Also referred to as 'coronary artery disease.'

Heart Block: a delay or complete block of the electrical impulse as it travels from the "sinus node" to the ventricles. The level of the block or delay may occur in the AV node or HIS-Purkinje system. The heartbeat may be irregular and slow. (Cleveland Clinic, Diseases & Conditions) Impaired conduction of cardiac impulse that can occur anywhere along the conduction pathway. Heart blocks can be classified by the duration, frequency, or completeness of conduction block. Reversibility depends on the degree of structural or functional defects. (MeSH)