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.

As an overall medical condition PVCs are normally not very harmful to patients that experience them, but frequent PVCs may put patients at increased risk of developing arrhythmias or cardiomyopathy, which can greatly impact the functioning of the heart over the span of that patient's life. On a more serious and severe scale, frequent PVCs can accompany underlying heart disease and lead to chaotic, dangerous heart rhythms and possibly sudden cardiac death.

Asymptomatic patients that do not have heart disease have long-term prognoses very similar to the general population, but asymptomatic patients that have ejection fractions greater than 40% have a 3.5% incidence of sustained ventricular tachycardia or cardiac arrest. One drawback comes from emerging data that suggests very frequent ventricular ectopy may be associated with cardiomyopathy through a mechanism thought to be similar to that of chronic right ventricular pacing associated cardiomyopathy. Patients that have underlying chronic structural heart disease and complex ectopy, mortality is significantly increased.

In meta-analysis of 11 studies, people with frequent PVC (≥1 time during a standard electrocardiographic recording or ≥30 times over a 1-hour recording) had risk of cardiac death 2 times higher than persons without frequent PVC. Although most studies made attempts to exclude high-risk subjects, such as those with histories of cardiovascular disease, they did not test participants for underlying structural heart disease.

In a study of 239 people with frequent PVCs (>1000 beats/day) and without structural heart disease (i.e. in the presence of normal heart function) there were no serious cardiac events through 5.6 years on average, but there was correlation between PVC prevalence and decrease of ejection fraction and increase of left ventricular diastolic dimension. In this study absence of heart of disease was excluded by echocardiography, cardiac magnetic resonance imaging in 63 persons and Holter monitoring.

Another study has suggested that in the absence of structural heart disease even frequent (> 60/h or 1/min) and complex PVCs are associated with a benign prognosis. It was study of 70 people followed by 6.5 years on average. Healthy status was confirmed by extensive noninvasive cardiologic examination, although cardiac catheterization of a subgroup disclosed serious coronary artery disease in 19%. Overall survival was better than expected.

On the other hand, the Framingham Heart Study reported that PVCs in apparently healthy people were associated with a twofold increase in the risk of all-cause mortality, myocardial infarction and cardiac death. In men with coronary heart disease and in women with or without coronary heart disease, complex or frequent arrhythmias were not associated with an increased risk. The at-risk people might have subclinical coronary disease. These Framingham results have been criticised for the lack of rigorous measures to exclude the potential confounder of underlying heart disease.

In the ARIC study of 14,783 people followed for 15 to 17 years those with detected PVC during 2 minute ECG, and without hypertension or diabetes on the beginning, had risk of stroke increased by 109%. Hypertension or diabetes, both risk factors for stroke, did not change significantly risk of stroke for people with PVC. It is possible that PVCs identified those at risk of stroke with blood pressure and impaired glucose tolerance on a continuum of risk below conventional diagnostic thresholds for hypertension and diabetes. Those in ARIC study with any PVC had risk of heart failure increased by 63% and were >2 times as likely to die due to coronary heart disease (CHD). Risk was also higher for people with or without baseline CHD.

In the Niigata study of 63,386 people with 10-year follow-up period those with PVC during a 10-second recording had risk of atrial fibrillation increased nearly 3 times independently from risk factors: age, male sex, body mass index, hypertension, systolic and diastolic blood pressure, and diabetes.

Reducing frequent PVC (>20%) by antiarrhythmic drugs or by catheter ablation significantly improves heart performance.

Recent studies have shown that those subjects who have an extremely high occurrence of PVCs (several thousand a day) can develop dilated cardiomyopathy. In these cases, if the PVCs are reduced or removed (for example, via ablation therapy) the cardiomyopathy usually regresses.

Also, PVCs can permanently cease without any treatment, in a material percentage of cases.

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

The following stimulants, conditions and triggers may increase your risk of the more frequent occurrence of premature ventricular contractions:

- Caffeine, tobacco and alcohol

- Exercise

- High blood pressure (hypertension)

- Anxiety

- Underlying heart disease, including congenital heart disease, coronary artery disease, heart attack, heart failure and a weakened heart muscle (cardiomyopathy)

- African American ethnicity- increased the risk of PVCs by 30% in comparison with the risk in white individuals

- Male sex

- Lower serum magnesium or potassium levels

- Faster sinus rates

- A bundle-branch block on 12-lead ECG

- Hypomagnesemia

- Hypokalemia

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

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

Knowledge that TdP may occur in patients taking certain prescription drugs has been both a major liability and reason for retirement of these medications from the marketplace. Examples of compounds linked to clinical observations of TdP include amiodarone, fluoroquinolones, methadone, lithium, chloroquine, erythromycin, amphetamine, ephedrine, pseudoephedrine, methylphenidate, and phenothiazines. It has also been shown as a side effect of certain anti-arrhythmic medications, such as sotalol, procainamide, and quinidine. The gastrokinetic drug cisapride (Propulsid) was withdrawn from the US market in 2000 after it was linked to deaths caused by long QT syndrome-induced torsades de pointes. In many cases, this effect can be directly linked to QT prolongation mediated predominantly by inhibition of the hERG channel.

In September 2011 (subsequently updated in March 2012 and February 2013), the FDA issued a warning concerning increased incidence of QT prolongation in patients prescribed doses of the antidepressant Celexa (citalopram) above 40 mg per day, considered the maximum allowable dosage, thereby increasing the risk of Torsades. However, a study, "Evaluation of the FDA Warning Against Prescribing Citalopram at Doses Exceeding 40 mg," reported no increased risk of abnormal arrhythmias, thus questioning the validity of the FDA's warning.

Sudden cardiac arrest is the leading cause of death in the industrialised world. It exacts a significant mortality with approximately 70,000 to 90,000 sudden cardiac deaths each year in the United Kingdom, and survival rates are only 2%. The majority of these deaths are due to ventricular fibrillation secondary to myocardial infarction, or "heart attack". During ventricular fibrillation, cardiac output drops to zero, and, unless remedied promptly, death usually ensues within minutes.

The true incidence of TIC is unclear. Some studies have noted the incidence of TIC in adults with irregular heart rhythms to range from 8% to 34%. Other studies of patients with atrial fibrillation and left ventricular dysfunction estimate that 25-50% of these study participants have some degree of TIC. TIC has been reported in all age groups.

Arrhythmia may be classified by rate (tachycardia, bradycardia), mechanism (automaticity, re-entry, triggered) or duration (isolated premature beats; couplets; runs, that is 3 or more beats; non-sustained= less than 30 seconds or sustained= over 30 seconds).

It is also appropriate to classify by site of origin:

Congenital heart defects are structural or electrical pathway problems in the heart that are present at birth. Anyone can be affected with this because overall health does not play a role in the problem. Problems with the electrical pathway of the heart can cause very fast or even deadly arrhythmias. Wolff–Parkinson–White syndrome is due to an extra pathway in the heart that is made up of electrical muscle tissue. This tissue allows the electrical impulse, which stimulates the heartbeat, to happen very rapidly. Right Ventricular outflow tract Tachycardia is the most common type of ventricular tachycardia in otherwise healthy individuals. This defect is due to an electrical node in the right ventricle just before the pulmonary artery. When the node is stimulated, the patient will go into ventricular tachycardia, which does not allow the heart to fill with blood before beating again. Long QT Syndrome is another complex problem in the heart and has been labeled as an independent factor in mortality. There are multiple methods of treatment for these including cardiac ablations, medication treatment, or altering your lifestyle to have less stress and exercise. It is possible to live a full and happy life with these conditions.

The following is a list of factors associated with an increased tendency towards developing torsades de pointes:

- Hypokalemia (low blood potassium)

- Hypomagnesemia (low blood magnesium)

- Hypocalcemia (low blood calcium)

- Bradycardia (slow heartbeat)

- Heart failure

- Left ventricular hypertrophy

- Hypothermia

- Subarachnoid hemorrhage

- Hypothyroidism

Although often regarded as a relatively benign heart rhythm problem, atrial flutter shares the same complications as the related condition atrial fibrillation. There is paucity of published data directly comparing the two, but overall mortality in these conditions appears to be very similar.

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.

Sudden death is not directly associated with atrial flutter. However, in individuals with a pre-existing accessory conduction pathway, such as the bundle of Kent in Wolff-Parkinson-White syndrome, the accessory pathway "may" conduct activity from the atria to the ventricles at a rate that the AV node would usually block. Bypassing the AV node, the atrial rate of 300 beats/minute leads to a ventricular rate of 300 beats/minute (1:1 conduction). Even if the ventricles are able to sustain a cardiac output at such a high rates, 1:1 flutter with time may degenerate into ventricular fibrillation, causing hemodynamic collapse and death.

Also known as chronic nonparoxysmal sinus tachycardia, patients have elevated resting heart rate and/or exaggerated heart rate in response to exercise. These patients have no apparent heart disease or other causes of sinus tachycardia. IST is thought to be due to abnormal autonomic control.

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.

Possible underlying causes, which may be treatable and reversible in certain cases, include the Hs and Ts.

- Hypovolemia

- Hypoxia

- Hydrogen ions (acidosis)

- Hypothermia

- Hyperkalemia or Hypokalemia

- Hypoglycemia

- Tablets or Toxins (drug overdose)

- Electric shock

- Tachycardia

- Cardiac Tamponade

- Tension pneumothorax

- Thrombosis (myocardial infarction or pulmonary embolism)

- Trauma (hypovolemia from blood loss)

While the heart is asystolic, there is no blood flow to the brain unless CPR or internal cardiac massage (when the chest is opened and the heart is manually compressed) is performed, and even then it is a small amount. After many emergency treatments have been applied but the heart is still unresponsive, it is time to consider pronouncing the patient dead. Even in the rare case that a rhythm reappears, if asystole has persisted for fifteen minutes or more, the brain will have been deprived of oxygen long enough to cause brain death.

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).

An electrocardiogram (ECG) is used to classify the type of tachycardia. They may be classified into narrow and wide complex based on the QRS complex. Presented order of most to least common, they are:

- Narrow complex

- Sinus tachycardia, which originates from the sino-atrial (SA) node, near the base of the superior vena cava

- Atrial fibrillation

- Atrial flutter

- AV nodal reentrant tachycardia

- Accessory pathway mediated tachycardia

- Atrial tachycardia

- Multifocal atrial tachycardia

- Junctional tachycardia

- Wide complex

- Ventricular tachycardia, any tachycardia that originates in the ventricles

- Any narrow complex tachycardia combined with a problem with the conduction system of the heart, often termed "supraventricular tachycardia with aberrancy"

- A narrow complex tachycardia with an accessory conduction pathway, often termed "supraventricular tachycardia with pre-excitation" (e.g. Wolff–Parkinson–White syndrome)

- Pacemaker-tracked or pacemaker-mediated tachycardia

Tachycardias may be classified as either narrow complex tachycardias (supraventricular tachycardias) or wide complex tachycardias. Narrow and wide refer to the width of the QRS complex on the ECG. Narrow complex tachycardias tend to originate in the atria, while wide complex tachycardias tend to originate in the ventricles. Tachycardias can be further classified as either regular or irregular.

For infants, bradycardia is defined as a heart rate less than 100 BPM (normal is around 120–160). Premature babies are more likely than full-term babies to have apnea and bradycardia spells; their cause is not clearly understood. The spells may be related to centers inside the brain that regulate breathing which may not be fully developed. Touching the baby gently or rocking the incubator slightly will almost always get the baby to start breathing again, which increases the heart rate. Medications (theophylline or caffeine) can be used to treat these spells in babies if necessary. Neonatal intensive-care unit (NICU) standard practice is to electronically monitor the heart and lungs for this reason.

These possible causes are remembered as the 6 Hs and the 6 Ts. See Hs and Ts

- Hypovolemia

- Hypoxia

- Hydrogen ions (Acidosis)

- Hyperkalemia or Hypokalemia

- Hypoglycemia

- Hypothermia

- Tablets or Toxins (Drug overdose)

- Cardiac Tamponade

- Tension pneumothorax

- Thrombosis (e.g., myocardial infarction, pulmonary embolism)

- Tachycardia

- Trauma (e.g., hypovolemia from blood loss)

This list is not fully comprehensive. Most notably, it does not include anaphylaxis. Pressure effects associated with artificial ventilation may also contribute to significant reduction in cardiac output, resulting in a clinical diagnosis of PEA.

The possible mechanisms by which the above conditions can cause pulseless in PEA or the same as those recognized as producing circulatory shock states. These are (1) impairment of cardiac filling, (2) impaired pumping effectiveness of the heart, (3) circulatory obstruction and (4) pathological vasodilation causing loss of vascular resistance and excess capacitance. More than one mechanism may be involved in any given case.

Ouabain infusion decreases ventricular escape time and increases ventricular escape rhythm. However, a high dose of ouabain can lead to ventricular tachycardia.

Ventricular fibrillation has been described as "chaotic asynchronous fractionated activity of the heart" (Moe et al. 1964). A more complete definition is that ventricular fibrillation is a "turbulent, disorganized electrical activity of the heart in such a way that the recorded electrocardiographic deflections continuously change in shape, magnitude and direction".

Ventricular fibrillation most commonly occurs within diseased hearts, and, in the vast majority of cases, is a manifestation of underlying ischemic heart disease. Ventricular fibrillation is also seen in those with cardiomyopathy, myocarditis, and other heart pathologies. In addition, it is seen with electrolyte imbalance, overdoses of cardiotoxic drugs, and following near drowning or major trauma. It is also notable that ventricular fibrillation occurs where there is no discernible heart pathology or other evident cause, the so-called idiopathic ventricular fibrillation.

Idiopathic ventricular fibrillation occurs with a reputed incidence of approximately 1% of all cases of out-of-hospital arrest, as well as 3%-9% of the cases of ventricular fibrillation unrelated to myocardial infarction, and 14% of all ventricular fibrillation resuscitations in patients under the age of 40. It follows then that, on the basis of the fact that ventricular fibrillation itself is common, idiopathic ventricular fibrillation accounts for an appreciable mortality. Recently described syndromes such as the Brugada Syndrome may give clues to the underlying mechanism of ventricular arrhythmias. In the Brugada syndrome, changes may be found in the resting ECG with evidence of right bundle branch block (RBBB) and ST elevation in the chest leads V1-V3, with an underlying propensity to sudden cardiac death.

The relevance of this is that theories of the underlying pathophysiology and electrophysiology must account for the occurrence of fibrillation in the apparent "healthy" heart. It is evident that there are mechanisms at work that we do not fully appreciate and understand. Investigators are exploring new techniques of detecting and understanding the underlying mechanisms of sudden cardiac death in these patients without pathological evidence of underlying heart disease.

Familial conditions that predispose individuals to developing ventricular fibrillation and sudden cardiac death are often the result of gene mutations that affect cellular transmembrane ion channels. For example, in Brugada Syndrome, sodium channels are affected. In certain forms of long QT syndrome, the potassium inward rectifier channel is affected.

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.