There are many causes of abnormal heart rhythms Causes Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart. Heart disorders are... read more 
(arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle, such as avoiding alcohol, caffeine (in beverages and foods), and smoking. Other arrhythmias are dangerous or bothersome enough to need treatment. An implantable cardioverter-defibrillator (ICD) is one type of treatment. Other treatments for arrhythmias include insertion of a pacemaker Artificial Pacemakers There are many causes of abnormal heart rhythms (arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle,... read more 
, cardioversion-defibrillation Cardioversion-Defibrillation There are many causes of abnormal heart rhythms (arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle,... read more 
, use of antiarrhythmic drugs Drugs to Treat Abnormal Heart Rhythms There are many causes of abnormal heart rhythms (arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle,... read more , or destruction of a small area of heart tissue that is responsible for the arrhythmia (ablation Destroying Abnormal Heart Tissue (Ablation) There are many causes of abnormal heart rhythms (arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle,... read more ).
Cardioversion and defibrillation Cardioversion-Defibrillation There are many causes of abnormal heart rhythms (arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle,... read more involve giving an electrical shock to the heart. Sometimes this shock can stop a fast arrhythmia and restore normal rhythm. The shock briefly stops the heart from beating and, after a second or two, it starts beating again on its own. Often, it starts back in a normal rhythm, but sometimes the arrhythmia starts again.
An implantable cardioverter-defibrillator (ICD), is a small defibrillator Cardioversion-Defibrillation There are many causes of abnormal heart rhythms (arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle,... read more that is about half the size of a deck of cards and can be placed inside the body. Most devices are implanted through the blood vessels just as a pacemaker Artificial Pacemakers There are many causes of abnormal heart rhythms (arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle,... read more is, thus eliminating the need for open chest surgery. Another type of ICD is placed under the skin rather than through the blood vessels. A wearable vest-like defibrillator is sometimes used if the person does not need an ICD for a long time.
ICDs continually monitor the rate and rhythm of the heart. They can identify fast and slow arrhythmias and deliver either a pacing treatment or a shock to convert the arrhythmia back to a normal rhythm. Most commonly, these devices are used in people who might otherwise die of the arrhythmia, such as people who have had life-threatening arrhythmias, including ventricular fibrillation Ventricular Fibrillation Ventricular fibrillation is a potentially fatal, uncoordinated series of very rapid, ineffective contractions of the ventricles (lower chambers of the heart) caused by many chaotic electrical... read more 
and some forms of ventricular tachycardia Ventricular Tachycardia Ventricular tachycardia is a heart rhythm that originates in the ventricles (lower chambers of the heart) and produces a heart rate of at least 120 beats per minute (the normal heart rate is... read more 
. Doctors may also place an ICD when people have certain heart disorders that are highly likely to cause life-threatening arrhythmias.
When an ICD delivers a shock, it can feel like a mild thump in the chest. When a stronger shock is given, people may feel as if they have been kicked. People do not feel shocks when the ICD acts as a pacemaker.
People who have ICDs can safely be around most home electronic devices, including microwaves, and airport security detectors. However, some equipment with strong magnetic fields or strong electric fields may interfere with ICDs. Examples are electrocautery devices used to stop bleeding during surgery, diathermy (physical therapy treatments that use radiowaves to apply heat to muscles), and sometimes MRI.
Because ICDs do not prevent arrhythmias, drugs often must be taken as well. These devices last for about 5 to 7 years. People with an ICD who experience a single shock from the device and who otherwise feel well should contact their ICD clinic or specialist within the week. The device records the person's heart rhythm, thus allowing the doctor to see why a shock was given. People who had other symptoms, such as shortness of breath, chest discomfort, or palpitations, immediately before or after the shock, or who had multiple shocks may have a more serious problem. Such people should go to the emergency department right away.
