The heart beats or pumps blood at a certain speed depending on the needs of the patient's body. When the heart is pumping normally, the heart is said to be in a normal (sinus) rhythm. Any deviation from a normal rhythm is defined as an arrhythmia, where the heart is beating too fast, too slow, beating irregularly or a combination of these abnormal rhythms.

Arrhythmias are generally divided between atrial arrhythmias such as atrial fibrillation and ventricular arrhythmias. Most arrhythmias can be treated with medications, but some require surgery. While most arrhythmias are not life-threatening, some, such as ventricular fibrillation, are fatal if not treated quickly. Arrhythmias can be secondary to many causes, such as heart attack, medications, and electrolyte imbalances.