Arrhythmias are abnormalities in the heart's rhythm, resulting from irregular electrical impulses that can lead to a heart rate that is too fast, too slow, or erratic. They are clinically significant as they can cause symptoms ranging from palpitations to syncope and may lead to serious complications such as stroke or sudden cardiac arrest. A common example is atrial fibrillation, which increases the risk of thromboembolic events due to ineffective atrial contraction.