Cardiac arrhythmia, also known as cardiac dysrhythmia or irregular heartbeat, is a group of conditions in which the heartbeat is irregular, too fast, or too slow. A heartbeat that is too fast - above 100 beats per minute in adults - is called tachycardia and a heartbeat that is too slow - below 60 beats per minute - is called bradycardia. Many arrhythmias have no symptoms. When symptoms are present these may include palpitations or feeling a pause between heartbeats.