Atrial fibrillation increases the risk of heart failure by 11 per 1000, kidney problems by 6 per 1000, death by 4 per 1000, stroke by 3 per 1000, and coronary heart disease by 1 per 1000. Women have a worse outcome overall than men. Evidence increasingly suggests that atrial fibrillation is independently associated with a higher risk of developing dementia.

Sinus tachycardia is usually a response to normal physiological situations, such as exercise and an increased sympathetic tone with increased catecholamine release—stress, fright, flight, anger. Other causes include:

- Pain

- Fever

- Anxiety

- Dehydration

- Malignant hyperthermia

- Hypovolemia with hypotension and shock

- Anemia

- Heart failure

- Hyperthyroidism

- Mercury poisoning

- Kawasaki disease

- Pheochromocytoma

- Sepsis

- Pulmonary embolism

- Acute coronary ischemia and myocardial infarction

- Chronic obstructive pulmonary disease

- Hypoxia

- Intake of stimulants such as caffeine, theophylline, nicotine, cocaine, or amphetamines

- Hyperdynamic circulation

- Electric shock

- Drug withdrawal

- Porphyria

- Acute inflammatory demyelinating polyradiculoneuropathy

- Postural orthostatic tachycardia syndrome

Inappropriate Sinus Tachycardia (IST) is a rare type of cardiac arrhythmia, within the category of supraventricular tachycardia (SVT). IST may be caused by the sinus node itself having an abnormal structure or function, or it may be part of a problem called dysautonomia, a disturbance and/or failure of the autonomic nervous system. Research into the mechanism and etiology (cause) of Inappropriate Sinus Tachycardia is ongoing.

IST is viewed by most to be a benign condition in the long-term. Symptoms of IST however, may be distracting and warrant treatment. The heart is a strong muscle and typically can sustain the higher-than-normal heart rhythm, though monitoring the condition is generally recommended.

The mechanism and primary etiology of Inappropriate Sinus Tachycardia has not been fully elucidated. An autoimmune mechanism has been suggested as several studies have detected autoantibodies that activate beta adrenoreceptors in a portion of patients. The mechanism of the arrhythmia primarily involves the sinus node and peri-nodal tissue and does not require the AV node for maintenance. Treatments in the form of pharmacological therapy or catheter ablation are available, although it is currently difficult to treat successfully.

Some causes of tachycardia include:

- Adrenergic storm

- Alcohol

- Amphetamine

- Anaemia

- Antiarrhythmic agents

- Anxiety

- Atrial fibrillation

- Atrial flutter

- Atrial tachycardia

- AV nodal reentrant tachycardia

- Brugada syndrome

- Caffeine

- Cocaine

- Exercise

- Fear

- Fever

- Hypoglycemia

- Hypovolemia

- Hyperthyroidism

- Hyperventilation

- Infection

- Junctional tachycardia

- Methamphetamine

- Multifocal atrial tachycardia

- Nicotine

- Pacemaker mediated

- Pain

- Pheochromocytoma

- Sinus tachycardia

- Tricyclic antidepressants

- Wolff–Parkinson–White syndrome

The cause of this condition is not accurately known, though it is probably of nervous origin and can be aggravated by physical wear and tear. The symptoms are sometimes very alarming but it is not considered in itself dangerous.

It has an increased risk of developing in WPW syndrome and LGL syndrome.

It can result in many abnormal heart rhythms (arrhythmias), including sinus arrest, sinus node exit block, sinus bradycardia, and other types of bradycardia (slow heart rate).

Sick sinus syndrome may also be associated with tachycardias (fast heart rate) such as atrial tachycardia (PAT) and atrial fibrillation. Tachycardias that occur with sick sinus syndrome are characterized by a long pause after the tachycardia. Sick sinus syndrome is also associated with azygos continuation of interrupted inferior vena cava.

Paroxysmal tachycardia is a form of tachycardia which begins and ends in an acute (or paroxysmal) manner.

It is also known as "Bouveret-Hoffmann syndrome".

The decreased heart rate can cause a decreased cardiac output resulting in symptoms such as lightheadedness, dizziness, hypotension, vertigo, and syncope. The slow heart rate may also lead to atrial, junctional, or ventricular ectopic rhythms.

Bradycardia is not necessarily problematic. People who regularly practice sports may have sinus bradycardia, because their trained hearts can pump enough blood in each contraction to allow a low resting heart rate. Sinus bradycardia can also be an adaptive advantage; for example, diving seals may have a heart rate as low as 12 beats per minute, helping them to conserve oxygen during long dives.

Sinus bradycardia is a common condition found in both healthy individuals and those who are considered well conditioned athletes.

Heart rates considered bradycardic vary by species; for example, in the common housecat, a rate of under 120 beats per minute is abnormal. Generally, smaller species have higher heart rates while larger species have lower rates.

Paroxysmal supraventricular tachycardia (PSVT) is a type of supraventricular tachycardia. Often people have no symptoms. Otherwise symptoms may include palpitations, feeling lightheaded, sweating, shortness of breath, and chest pain. Episodes start and end suddenly.

The cause is not known. Risk factors include alcohol, caffeine, nicotine, psychological stress, and Wolff-Parkinson-White syndrome which often is inherited from a person's parents. The underlying mechanism typically involves an accessory pathway that results in re-entry. Diagnosis is typically by an electrocardiogram (ECG) which shows narrow QRS complexes and a fast heart rhythm typically between 150 and 240 beats per minute.

Vagal maneuvers, such as the valsalva maneuver, are often used as the initial treatment. If not effective and the person has a normal blood pressure the medication adenosine may be tried. If adenosine is not effective a calcium channel blockers or beta blocker may be used. Otherwise synchronized cardioversion is the treatment. Future episodes can be prevented by catheter ablation.

About 2.3 per 1000 people have paroxysmal supraventricular tachycardia. Problems typically begin in those 12 to 45 years old. Women are more often affected than men. Outcomes in those who otherwise have a normal heart are generally good. An ultrasound of the heart may be done to rule out underlying heart problems.

Sick sinus syndrome is a relatively uncommon syndrome in the young and middle age population. Sick sinus syndrome is more common in elderly adults, where the cause is often a non-specific, scar-like degeneration of the cardiac conduction system. Cardiac surgery, especially to the atria, is a common cause of sick sinus syndrome in children.

Atrial bradycardias are divided into three types. The first, respiratory sinus arrhythmia, is usually found in young and healthy adults. Heart rate increases during inhalation and decreases during exhalation. This is thought to be caused by changes in the vagal tone during respiration. If the decrease during exhalation drops the heart rate below 60 bpm on each breath, this type of bradycardia is usually deemed benign and a sign of good autonomic tone.

The second, sinus bradycardia, is a sinus rhythm of less than 60 BPM. It is a common condition found in both healthy individuals and those considered well-conditioned athletes. Studies have found that 50–85% of conditioned athletes have benign sinus bradycardia, as compared to 23% of the general population studied. The heart muscle of athletes has become conditioned to have a higher stroke volume, so requires fewer contractions to circulate the same volume of blood.

The third, sick sinus syndrome, covers conditions that include severe sinus bradycardia, sinoatrial block, sinus arrest, and bradycardia-tachycardia syndrome (atrial fibrillation, flutter, and paroxysmal supraventricular tachycardia).

MAT usually arises because of an underlying medical condition. Its prevalence has been estimated at about 3 per 1000 in adult hospital inpatients and is much rarer in paediatric practice; it is more common in the elderly, and its management and prognosis are both those of the underlying diagnosis.

It is mostly common in patients with lung disorders, but it can occur after acute myocardial infarction and can also occur in the setting of low blood potassium or low blood magnesium.

It is sometimes associated with digitalis toxicity in patients with heart disease.

It is most commonly associated with hypoxia and COPD. Additionally, it can be caused by theophylline toxicity, a drug with a narrow therapeutic index commonly used to treat COPD. Theophylline can cause a number of different abnormal heart rhythms when in excess, and thus further predisposes COPD patients to MAT. Theophylline toxicity often occurs following acute or chronic overtreatment or factors lowering its clearance from the body.

Treatment depends on the origin of the automatic tachycardia, however the mainstay of treatment is either antidysrhythmic medication or cardiac pacing. Specifically overdrive pacing may be used for all forms of automatic tachycardia; a pacemaker assumes control of the heart rhythm in overdrive pacing. In some cases ablation of the ectopic focus may be necessary.

If the person is hemodynamically unstable or other treatments have not been effective, synchronized electrical cardioversion may be used. In children this is often done with a dose of 0.5 to 1 J/Kg.

Symptoms reported by patients vary in frequency and severity.

Symptoms associated with IST include:

- Frequent or sustained palpitations

- Dyspnea (shortness of breath) and palpitations on exertion

- Pre-syncope (feeling as if about to faint)

- Fatigue (physical)

- Dizziness

- Exercise intolerance

- Occasional paresthesia and cramping

- Symptoms associated with autonomic nervous system disturbance, including GI disturbance

Bradycardia in an adult is any heart rate less than (BPM), although symptoms usually manifest only for heart rates less than 50 BPM.

A family history of AF may increase the risk of AF. A study of more than 2,200 people found an increased risk factor for AF of 1.85 for those that had at least one parent with AF. Various genetic mutations may be responsible.

Four types of genetic disorder are associated with atrial fibrillation:

- Familial AF as a monogenic disease

- Familial AF presenting in the setting of another inherited cardiac disease (hypertrophic cardiomyopathy, dilated cardiomyopathy, familial amyloidosis)

- Inherited arrhythmic syndromes (congenital long QT syndrome, short QT syndrome, Brugada syndrome)

- Non-familial AF associated with genetic backgrounds (polymorphism in the ACE gene) that may predispose to atrial fibrillation

Palpitation can be attributed to one of four main causes:

1. Extra-cardiac stimulation of the sympathetic nervous system (inappropriate stimulation of the sympathetic nervous system, particularly the vagus nerve (which innervates the heart), can be caused by anxiety and stress due to acute or chronic elevations in glucocorticoids and catecholamines. Gastrointestinal distress such as bloating or indigestion, along with muscular imbalances and poor posture, can also irritate the vagus nerve causing palpitations)

2. Sympathetic overdrive (panic disorders, low blood sugar, hypoxia, antihistamines (i.e. levocetirizine), low red blood cell count, heart failure, mitral valve prolapse).

3. Hyperdynamic circulation (valvular incompetence, thyrotoxicosis, hypercapnia, high body temperature, low red blood cell count, pregnancy).

4. Abnormal heart rhythms (ectopic beat, premature atrial contraction, junctional escape beat, premature ventricular contraction, atrial fibrillation, supraventricular tachycardia, ventricular tachycardia, ventricular fibrillation, heart block).

Symptoms are typically precipitated ("triggered") by exercise-induced ventricular arrhythmias during periods of physical activity or acute emotional stress.

Atrioventricular reentrant tachycardia, atrioventricular reciprocating tachycardia or AVRT, is a type of abnormal fast heart rhythm and is classified as a type of supraventricular tachycardia (SVT). AVRT is most commonly associated with Wolff-Parkinson-White syndrome, in which an accessory pathway allows electrical signals from the heart's ventricles to enter the atria and cause earlier than normal contraction, which leads to repeated stimulation of the atrioventricular node.

Sinus tachycardia (also colloquially known as sinus tach or sinus tachy) is a sinus rhythm with an elevated rate of impulses, defined as a rate greater than 100 beats/min (bpm) in an average adult. The normal resting heart rate in the average male adult ranges from 60–100 bpm and women 60-90bpm. Note that the normal heart rate varies with age, with infants having normal heart rate of 110–150 bpm, in contrast to the elderly, who have slower normals.

The upper threshold of a normal human resting heart rate is based on age. Cutoff values for tachycardia in different age groups are fairly well standardized; typical cutoffs are listed below:

- 1–2 days: Tachycardia > 159 beats per minute (bpm)

- 3–6 days: Tachycardia >166 bpm

- 1–3 weeks: Tachycardia >182 bpm

- 1–2 months: Tachycardia >179 bpm

- 3–5 months: Tachycardia >186 bpm

- 6–11 months: Tachycardia >169 bpm

- 1–2 years: Tachycardia >151 bpm

- 3–4 years: Tachycardia >137 bpm

- 5–7 years: Tachycardia >133 bpm

- 8–11 years: Tachycardia >130 bpm

- 12–15 years: Tachycardia >119 bpm

- >15 years – adult: Tachycardia >100 bpm

Heart rate is considered in the context of the prevailing clinical picture. For example: in sepsis >90 bpm is considered tachycardia.

When the heart beats excessively or rapidly, the heart pumps less efficiently and provides less blood flow to the rest of the body, including the heart itself. The increased heart rate also leads to increased work and oxygen demand by the heart, which can lead to rate related ischemia.

Relative tachycardia involves a greater increase in rate than would be expected in a given illness state.

Ventricular tachycardia can occur due to coronary heart disease, aortic stenosis, cardiomyopathy, electrolyte problems (e.g., low blood levels of magnesium or potassium), inherited channelopathies (e.g., long-QT syndrome), catecholaminergic polymorphic ventricular tachycardia, arrhythmogenic right ventricular dysplasia, or a heart attack.

An automatic tachycardia is a cardiac arrhythmia which involves an area of the heart generating an abnormally fast rhythm, sometimes also called enhanced automaticity. These tachycardias, or fast heart rhythms, differ from reentrant tachycardias (AVRT and AVNRT) in which there is an abnormal electrical pathway which gives rise to the pathology. Most automatic tachycardias are supraventricular tachycardias (SVT). It is important to recognise an automatic tachycardia because the treatment will be different to that for a reentrant tachycardia. The most useful clue will be the presence of 'warm up' and 'cool down'. This means that whereas a reentrant tachycardia will both begin and end abruptly as cardiac conduction utilises then ceases to utilise the accessory pathway, an automatic tachycardia will rise and fall gradually in rate as the automatic focus increases and decreases its automatic rate of electrical discharge.

Therapy may be directed either at terminating an episode of the abnormal heart rhythm or at reducing the risk of another VT episode. The treatment for stable VT is tailored to the specific person, with regard to how well the individual tolerates episodes of ventricular tachycardia, how frequently episodes occur, their comorbidities, and their wishes. Individuals suffering from pulseless VT or unstable VT are hemodynamically compromised and require immediate electric cardioversion to shock them out of the VT rhythm.