Classification
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).Arrhythmias are also classified by site of origin:

Atrial arrhythmia
Sinus bradycardia
Sinus arrhythmia
Sinus tachycardia
Premature atrial contractions (PACs)
Wandering atrial pacemaker
Atrial tachycardia
Multifocal atrial tachycardia
Supraventricular tachycardia (SVT)
Atrial flutter
Atrial fibrillation (Afib)
AV nodal reentrant tachycardia

Junctional arrhythmia
AV nodal reentrant tachycardia
Junctional rhythm
Junctional tachycardia
Premature junctional contraction

Ventricular arrhythmia
Premature ventricular contractions (PVCs), sometimes called ventricular extra beats (VEBs)
Premature ventricular beats occurring after every normal beat are termed ventricular bigeminy
PVCs that occur at intervals of 2 normal beats to 1 PVC, or 1 normal beat to 2 PVCs, are termed "PVCs in trigeminy"
Groups of three premature ventricular beats are called triplets and are considered a brief run of non-sustained ventricular tachycardia (NSVT); if the grouping lasts for more than 30 seconds, it is considered sustained ventricular tachycardia (VT). Accelerated idioventricular rhythm
Monomorphic ventricular tachycardia
Polymorphic ventricular tachycardia
Ventricular fibrillation
Torsades de pointes
Arrhythmogenic right ventricular dysplasia
Re-entry ventricular arrhythmia

Heart blocks
These are also known as AV blocks, because the vast majority of them arise from pathology at the atrioventricular node. They are the most common causes of bradycardia:
First-degree heart block, which manifests as PR prolongation
Second-degree heart block
Type 1 Second degree heart block, also known as Mobitz I or Wenckebach
Type 2 Second degree heart block, also known as Mobitz II
Third-degree heart block, also known as complete heart blockFirst, second, and third-degree blocks also can occur at the level of the sinoatrial junction.
Signs and symptoms
The term cardiac arrhythmia covers a very large number of very different conditions.The most common symptom of arrhythmia is an awareness of an abnormal heartbeat, called palpitations. These may be infrequent, frequent, or continuous. Some of these arrhythmias are harmless (though distracting for patients) but some of them predispose to adverse outcomes.Some arrhythmias do not cause symptoms and are not associated with increased mortality. However, some asymptomatic arrhythmias are associated with adverse events. Examples include a higher risk of blood clotting within the heart and a higher risk of insufficient blood being transported to the heart because of a weak heartbeat. Other increased risks are of embolization and stroke, heart failure, and sudden cardiac death.If an arrhythmia results in a heartbeat that is too fast, too slow, or too weak to supply the bodys needs, this manifests as lower blood pressure and may cause lightheadedness, dizziness, syncope or brain death due to insufficient supply of blood to the brain.Some types of arrhythmia result in cardiac arrest, or sudden death.Medical assessment of the abnormality using an electrocardiogram is one way to diagnose and assess the risk of any given arrhythmia. Mechanism
Cardiac arrhythmia are caused by one of two major mechanism. The first of arrhythmia is a result of enhanced or abnormal impulse formation originating at the pacemaker or the His-Purkinje network. The second is due to reentry conduction disturbances. Diagnostic
Cardiac arrhythmia is often first detected by simple but nonspecific means: auscultation of the heartbeat with a stethoscope, or feeling for peripheral pulses.