Arrhythmia or dysrhythmia refers to an abnormal heart rhythm caused by a defect in the heart's conduction system. It can cause the heart to beat irregularly, too quickly, or too slowly, leading to symptoms like chest pain, shortness of breath, and fainting. Factors such as stress, caffeine, alcohol, nicotine, cocaine, certain drugs, congenital defects, diseases, and electrolyte abnormalities can trigger arrhythmias.

Arrhythmias are categorized by their speed, rhythm, and origin. A slow heart rate (below 50 beats per minute) is called bradycardia, a rapid heart rate (over 100 beats per minute) is called tachycardia, and uncoordinated heartbeats are called arrhythmias. Arrhythmias originating in the atria are atrial arrhythmias, and those starting in the ventricles are ventricular arrhythmias.

Supraventricular tachycardia (SVT) results in a rapid but regular heart rate originating in the atria. Heart block occurs when the electrical pathways between the atria and ventricles are altered, with the most common site being the atrioventricular (AV) node. An atrial premature contraction (APC) is a heartbeat that occurs earlier than expected, briefly interrupting the normal rhythm. Atrial fibrillation (AF) is a common arrhythmia where atrial pumping ceases altogether.

Atrial flutter is a type of arrhythmia characterized by rapid, regular atrial contractions typically leading to a sawtooth pattern on an electrocardiogram and potentially resulting in an elevated heart rate and compromised cardiac function.

Treatment for arrhythmias involves antiarrhythmic drugs and radiofrequency ablation. In severe cases like VF, treatment includes cardiopulmonary resuscitation (CPR) and defibrillation, a process where a strong, brief electrical current is passed to the heart to stop the fibrillation. High-risk patients can receive an automatic implantable cardioverter defibrillator (AICD), a device that monitors heart rhythm and delivers a small shock directly to the heart when a life-threatening rhythm disturbance occurs. Automated external defibrillators (AEDs) are available for emergency response teams and public places.