What are arrhythmias? Arrhythmia is the medical name for a disorder of your heart rate (pulse) or heart rhythm, such as beating too fast (tachycardia) or too slow (bradycardia). An irregular heartbeat is another sign of an arrhythmia. Arrhythmias are caused by an abnormality in the conduction of nerve signals (impulses) within the heart muscle that affects the way the heart beats. Most arrhythmias are harmless, but others can be serious or even life threatening. If the heart rate is too fast, too slow, or irregular, the heart may not be able to effectively pump enough blood to the body. Lack of blood flow can damage the brain, heart, and other organs due to a lack of oxygen. The signs and symptoms of arrhythmias can be brief or last indefinitely. Some people have no symptoms at all, while others may have severe arrhythmia symptoms that compromise the cardiopulmonary system. Some arrhythmias are life threatening, but fortunately, arrhythmia treatment is successful in most cases. Left untreated, heart arrhythmias may lead to chest pain, heart attack, heart failure, and stroke. Seek immediate medical care (call 911) for serious symptoms, such as severe chest pain or pressure, sweating, and severe difficulty breathing, which may be combined with pale or bluish lips, fast heart rate, and anxiety. Seek prompt medical care if you are being treated for an arrhythmia but mild symptoms, such as fatigue, palpitations, or an irregular heartbeat, recur or are persistent.