Atrial flutter is a supraventricular tachydysrhythmia believed to arise from electrophysiologic disturbances in the atria. It tends to be an unstable rhythm and is usually associated with intrinsic cardiac or pulmonary disease or adverse extrinsic influences on the heart. It is due to either a reentry mechanism or an increased atrial automaticity. Atrial depolarization is regular at a rate of 260 to 340 beats per minute. With a normal atrioventricular (AV) node there is usually a physiologic second-degree block with resultant 2:1 conduction. Higher degrees of AV block can occur in patients with AV nodal disease, increased vagal tone, or when certain drugs are in use. One-to-one conduction may occur in patients with accessory AV nodal pathways. In this situation, serious adverse effects are often seen, including palpitations, dizziness, syncope, angina, and dyspnea. Electrical cardioversion is the safest and most reliable way of terminating atrial flutter and its use should not be delayed in an unstable patient. In the nonemergent situation a variety of medications alone or in combination can be used to convert the rhythm or slow ventricular response.