This article presents information on the shock therapy for heart ailments. Sudden cardiac arrest kills more than 300,000 Americans each year, more than breast cancer, prostate cancer, AIDS, house fires, handguns and traffic accidents combined. Unlike a heart attack, which is caused by blocked coronary arteries, sudden cardiac arrest occurs when the heart muscle unexpectedly spasms and can no longer pump blood. Defibrillation sends electrical current through the heart in an attempt to shock muscle fibers back into a normal rhythm. The defibrillator delivers 150 joules of energy, the amount required to power a 150-watt light bulb for 1 second.