Arrhythmias are extremely common. They are usually benign but their significance depends on the symptoms they cause. Some arrhythmias are more serious and can be life-threatening. In this article we clarify the causes of arrhythmias and help you sort out the different types that can occur, dividing them into the two main categories – tachyarrhythmias, where the heart rate is faster than normal, and bradyarrhythmias, where the heart rate is much slower than normal.