Amiodarone is a medication used to treat and prevent certain types of serious, life-threatening ventricular arrhythmias, which are a certain type of abnormal heart rhythm when other medications did not help or could not be tolerated. It is also used to treat atrial fibrillation. Amiodarone belongs to a group of medications called antiarrhythmics, and it works by blocking certain electrical signals in the heart that can cause an irregular heartbeat. It is known to relax overactive heart muscles. Amiodarone is available under the brand names Cordarone and Pacerone. It is usually taken once or twice a day, with or without food, but it is important to take it the same way each time. It is important to read the medication guide provided by your pharmacist before you start using amiodarone and each time you get a refill. Amiodarone can cause dangerous side effects on your heart, liver, lungs, or thyroid, so it is important to tell your doctor about any pre-existing conditions before taking it.