Atrial flutter is an abnormal heart rhythm, often described as a fast and regular beating. It is an irregular ECG, as it is characterized by an abnormal electrical activity in the atria of the heart. The atria beat too fast and too regularly, resulting in an abnormal rhythm. The ventricles then beat in a slower and irregular pattern, which is seen on the ECG. Atrial flutter is usually treated with medications or, in more severe cases, with a procedure called ablation.