Arrhythmias or dysrhythmias are abnormal heartbeats. An extra heartbeat is called a premature contraction. A fast heart rate is called tachycardia. A slow heart rate is called bradycardia. On very rare occasions, arrhythmias can be life-threatening medical emergencies. On the other hand, arrhythmias in young people with normal hearts are usually benign and require no treatment at all. Most children and young adults will experience some type of arrhythmia, which is usually transitory.
Normal Electrical Conduction in the Heart