Harvard Heart Letter

Ask the doctor: Atrial fibrillation vs. atrial flutter

Q. What's the difference between atrial flutter and atrial fibrillation?

A. Both of these heart-rhythm disorders arise from electrical misfires in the heart's upper chambers, or atria. The symptoms are often similar—mainly palpitations and lightheadedness. The conditions can occur together, and both are treated with either drugs or procedures that restore the heart's normal rhythm. But there are a few key differences.

Atrial flutter occurs when an extra or early beat initiates an abnormal electrical impulse that zips around the right atrium in a circular loop up to 300 times a minute. The atrioventricular (AV) node, which delivers the "pump now" signal to the heart's lower chambers (ventricles), usually blocks about half of these signals. The ventricles then contract about 150 times a minute, or about twice as fast as normal. During atrial flutter, a person's heartbeat tends to be rapid but regular.

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