While CPR classes tend to focus on helping someone who is experiencing cardiac arrest, first aid classes tend to focus on all other emergency situations: cuts, fractures, choking and everything in between. Taking both of these classes can be extremely beneficial in the event an emergency situation arises.  An automated external defibrillator (AED) is a medical device designed to analyze the heart rhythm and deliver an electric shock to victims of ventricular fibrillation to restore the heart rhythm to normal. Ventricular fibrillation is the uncoordinated heart rhythm most often responsible for sudden cardiac arrest.