Implantable cardioverter defibrillators (ICD) are devices that save the lives of patients at high risk of ventricular tachycardia or fibrillation.A tachycardia is a very fast heartbeat of more than 100 beats per minute. During tachycardia of the ventricles – the two main chambers of the heart – the heart beats too fast to pump sufficient blood to the body. This is life threatening and can lead to ventricular fibrillation. During ventricular fibrillation, the heart chambers can no longer contract. This causes cardiac arrest within minutes – the heart suddenly and unexpectedly stops beating – and is one of the most common causes of sudden cardiac death. The only way to stop ventricular fibrillation is defibrillation. An electric shock, defibrillation disrupts the tachycardia, allowing the heart to restart its activity in a normal rhythm. People who do not have an ICD can be defibrillated externally in an emergency. ICDs offer patients at high risk of ventricular tachycardia or fibrillation the best protection against these life-threatening events. An implantable defibrillator works around the clock to automatically detect irregularities in your heartbeat and deliver the appropriate treatment. It stops life-threatening tachycardia and fibrillation with relatively weak and painless stimulation therapy or electrical shocks. Minor surgery is necessary to implant an ICD.