An arrhythmia is any disorder of your heart rate or rhythm. It means that your heart beats too quickly, too slowly, or with an irregular pattern. Most arrhythmias result from problems in the electrical system of the heart. If your arrhythmia is serious, you may need a cardiac pacemaker or an implantable cardioverter defibrillator (ICD). They are devices that are implanted in your chest or abdomen.