Arrhythmia is an irregular heartbeat. There are several ways in which a heartbeat can lose its regular rhythm. These include tachycardia, when the heart beats too fast; bradycardia, when the heart beats too slowly; premature ventricular contractions, or additional, abnormal beats; fibrillation, when the heartbeat is irregular. Arrhythmias occur when electrical impulses in the heart that coordinate the heartbeat do not work properly. These make the heart beat in a way it should not, whether that be too fast, too slowly, or too erratically. Irregular heartbeats are common, and all people experience them. They feel like a fluttering or a racing heart. However, when they change too much or occur because of a damaged or weak heart, they need to be taken more seriously and treated. Arrhythmias can become fatal.