Atrial flutter/tachycardia : A regular, rhythmic tachycardia confined to the atria. The atrial rate durng this arrhythmia is over 220 beats/minute, and typically is about 300 beats/minute. As in ventricular tachycardia, atrial flutter is caused by a reentrant rhythm (spiral wave) in either the right or left atrium or both (as shown in the figure). In atrial flutter, the ventricles do not beat as rapidly as the atria because the AV node, acting as a safety valve, prevents most of the atrial beats from exciting the ventricles. Although the atria do not contract effectively, this type of arrhythmia is not immediately life-threatening. However, it can lead to other heart problems if not treated.