ICDs and pacemakers compared

Implantable cardioverter defibrillators (ICDs) work differently than pacemakers do. Both devices are implanted under the skin and have wires called "electrodes" leading to the heart. Both devices send electrical signals to the heart to keep it beating normally. But ICDs can give a much more powerful jolt to the heart if it starts to beat in a dangerous way. Pacemakers cannot do that.