Which of the following is NOT a lateral lead?

In the context of electrocardiography, lateral leads are those that primarily reflect electrical activity occurring in the left side of the heart, particularly in the left atrium and left ventricle. The lateral leads include Lead I, aVL, and V5, which are positioned in such a way that they monitor this region.

Lead I is derived from the potential difference between two limb electrodes and is positioned horizontally, evaluating the heart's electrical activity from the left to the right side. Similarly, aVL (augmented Vector Left) also looks at the left side of the heart but from a different angle, while V5, located on the left side of the chest, focuses on the lateral aspect of the heart.

Lead III, on the other hand, is oriented in a way that evaluates the inferior wall of the heart by measuring the electrical activity between the left arm and the left leg. Since it does not focus on the lateral aspects of the heart, Lead III is not classified as a lateral lead.

Therefore, identifying Lead III as the lead that does not belong with the others as a lateral lead is accurate given its positioning and the region of the heart it represents.