Multaq is used if you have had some type of irregular heartbeat (paroxysmal or persistent atrial fibrillation) in the past but now your heart rate is normal. Medicines help you keep your heart rhythm normal and reduce the risk of atrial fibrillation again. Multaq is known as an antiarrhythmic drug, this medicine should not be used if you have permanent atrial fibrillation because of the increased risk of very serious side effects.