Abnormalities of the heartbeat.  Can be caused by heart disease, congenital heart defects, overweight, caffeine, and some drugs.  Palpitations can feel like fluttering, pounding, or racing.  Can cause light headedness, shortness of breath, chest pain, or fainting.  Some types of arrhythmias can be treated with antiarrhythmic drugs, such as beta blockers, ion channel blockers, and drugs that prolong repolarization.  Defibrillation or cardioversion, which involves administering short electric shock to the heart, can sometimes be used to restore the heartbeat to normal.  For continual tachycardia, radiofrquency ablation (a nonsurgical technique that uses radio waves) can be used to remove diseased tissue and restore a normal rhythm.  In cases of low heart rate, a cardiac pacemaker may be fitted.