A CRT-D is an implantable cardiac resynchronization therapy (CRT) defibrillator for patients with heart failure . The device monitors the heart's rhythm, detects irregularities and corrects them with electrical impulses. Like an implantable defibrillator (ICD), a CRT-D is designed to stop life-threatening ventricular tachycardia and fibrillation with relatively weak and painless stimulation therapy or electrical shocks. CRT-Ds differ from ICDs in that they help your heart’s lower chambers – the ventricles – work in tandem. To do this, CRT-Ds have three leads – wires that deliver energy to the heart – rather than one or two, as in an ICD. A CRT-P is a cardiac resynchronization therapy pacemaker that does not have the defibrillation capabilities of a CRT-D. CRT-Ds enhance diseased hearts’ effectiveness and increase blood flow. They improve heart failure symptoms like fatigue, shortness of breath and exercise intolerance. Cardiac resynchronization therapy significantly lowers the risk of life-threatening cardiac events. Many patients’ quality of life improves significantly with a CRT-D. Surgery is necessary to implant a CRT-D.