Under normal circumstances, the rhythm of the heartbeat should be regular and neat, 60-100 beats per minute in adults. When the heartbeat loses its original rhythm and becomes too slow, too fast, or unevenly fast or slow, it is called an arrhythmia. Arrhythmias can occur at any age and are divided into two categories: fast arrhythmias, such as premature beats, tachycardia, atrial flutter, atrial fibrillation, ventricular flutter, and ventricular fibrillation; and slow arrhythmias, such as atrioventricular block, intraventricular block (bundle branch block), and sinus bradycardia.