Sudden cardiac death represents an enormous public health problem in all developed countries of the world. In the United States, sudden cardiac death occurs in more than 400,000 people each year and is the leading cause of death. In sudden cardiac death, the heart abruptly and unexpectedly ceases to function (cardiac arrest), presumably because of an electrical disturbance. Individuals deemed high risk for sudden cardiac death may be treated with implantable defibrillators. This article highlights evidence from randomized, controlled trials of implantable device therapy used in prevention of sudden cardiac death.