Palpitations are a symptom described as the sensation of having an irregular heart beat. This is a fairly common symptom that just about everyone experiences at one time or another. Palpitations occur when the heart beats irregularly. Whether or not palpitations are of medical concern is ultimately determined by medical history, physical exam findings, and testing. Most people know when it's time to go to see their physician because the palpitations have become sustained and very uncomfortable, or they are associated with another symptom such as shortness of breath.
Heart rhythm is controlled by factors both intrinsic and extrinsic to the heart itself.
Additionally, certain drugs and toxins can affect heart rhythm as well. The classification of abnormal heart rhythm, or dysrhythmia, is too complex to describe here. However, despite this complexity, some basic information can be given. The heart has an amazing ability to tolerate markedly abnormal rhythms. In fact, a double-blind study had to be discontinued because it was found that the group taking the antiarrhythmic drug was experiencing more deaths than the group taking the placebo.