What is an implanted cardioverter-defibrillator, and who needs one?

Learn how these high-tech devices can save — and change — your life.

Defibrillators are devices that can detect — and correct — potentially deadly heart rhythms. The most common is ventricular fibrillation, which makes the heart's lower chambers (ventricles) quiver without actually squeezing and pumping. Blood stops flowing to the brain and other organs, causing the person to pass out. Death can occur within minutes.

A quick jolt of electricity can restore the heart's normal rhythm, however. The shock can be delivered from outside the chest with an automated external defibrillator (AED). Located in many public places, these portable devices can be used by medical personnel as well as untrained people, thanks to audible prompts that explain what to do. But some people are candidates for an implantable cardioverter-defibrillator (ICD), a miniature electronic device placed under the skin below the collarbone (see illustration).