Occasional extra heartbeats, which are known as extrasystole, are not dangerous, according to MedlinePlus. These extra heartbeats are a type of heart palpitation, which occur when a person is aware of his own heartbeat, often feeling as if the heartbeat is racing or skipping beats.
Heart palpitations, including instances of extrasystole, can be caused by stress, panic attacks, exercise or fever. Ingesting substances such as caffeine, nicotine, cocaine, diet pills or other illegal drugs can also precipitate palpitations, as MedlinePlus explains. When palpitations are accompanied by an abnormal heart rhythm, they may be cause for concern. A patient who feels more than six extra heartbeats per minute or who experiences extra heartbeats coming in groups of three or more should contact his physician.