About 300,000 people die each year because their heart rhythm suddenly changes, causing the heart to quiver rather than pump blood effectively. A surgically implanted device known as an implantable cardioverter defibrillator (ICD) can deliver an electrical shock to the heart that restores its normal rhythm. A recent study, the Multicenter Automatic Defibrillator Implantation Trial (MADIT)-II, compared patients who received an ICD with a matched group who did not. This trial indicated that many patients who would not previously have received an ICD could benefit from its use. The problem is that ICD implantation is very expensive and should be used only in those most likely to benefit.