Final answer:
Atrial flutter most commonly occurs in the right atrium of the heart, where an ectopic focus overtakes the normal rhythm established by the sinoatrial (SA) node.
Step-by-step explanation:
Atrial flutter most commonly occurs in the right atrium of the heart. This condition is a type of supraventricular tachycardia characterized by a rapid and regular heart rate originating above the ventricles. The sinoatrial (SA) node, often referred to as the pacemaker of the heart, has the highest inherent rate of depolarization and establishes the normal cardiac rhythm. It is located in the superior and posterior walls of the right atrium, near the orifice of the superior vena cava. However, in atrial flutter, an ectopic focus within the right atrium can usurp the SA node's role, leading to a rapid rhythm that can be seen on an electrocardiogram (ECG).