MODEL RELEASED. Mid-air defibrillation. Cardiac arrest (heart attack) patient on an airliner receiving treatment with a defibrillator. This device treats ventricular fibrillation (uncoordinated twitching of heart muscle in the heart's ventricles) by applying an electric shock to restart the heart's normal rhythm. Fibrillation prevents the heart working effectively and is the main cause of death in heart attacks. The defibrillator being used is a model designed to be easy to operate for occasional users. Many commercial airlines carry defibrillators on all their flights.