Lead III primarily records the electrical difference between which two limbs?

Lead III in an electrocardiogram (ECG) primarily measures the electrical potential difference between the right arm and the left leg. In the standard 12-lead ECG configuration, leads are designated based on the specific anatomical locations from which they record electrical activity.

For Lead III, the positive electrode is placed on the left leg, while the negative electrode is on the right arm. This configuration allows Lead III to capture the electrical activity of the heart as it spreads from the right atrium towards the left ventricle, effectively providing insight into the inferior aspect of the heart.

Understanding lead placements is crucial for interpreting an ECG accurately. Lead III is significant in assessing heart rhythm and detecting abnormalities that may occur, such as arrhythmias or conduction issues, especially in the inferior wall of the heart.

The other possible pairings do not correspond to Lead III's configuration and would lead to confusion in readings or interpretations of the heart's electrical activity.