MODEL RELEASED. Defibrillator electrodes held by a hospital doctor. This equipment is used on patients who are having a heart attack (myocardial infarction). When this occurs, the heart's normal rhythm is disturbed and the heart can no longer pump blood around the body. This causes a loss of blood flow and a state of unconsciousness, which can prove fatal, unless the heart's rhythm can be restored. The metal plates on the defibrillator are placed on a patient's chest and an electric current passed through them. This may shock the heart into beating in a normal manner.