What is the placement instruction for V3 lead?

The placement instruction for the V3 lead is to position it equidistant between the V2 and V4 leads. This placement is crucial for accurately recording the electrical activity of the heart from specific areas of the chest.

The V3 lead is positioned in a location that allows it to capture the heart's signals from the same plane as the V2 and V4 leads, which are located on the left side of the chest. By placing V3 equidistant from these two leads, it ensures a comprehensive view of the heart's electrical activity in that region, which is particularly important for detecting abnormalities in the anterior wall of the left ventricle.

In the context of the other options, the midclavicular line position identifies a different area of the chest that may not provide the same level of detail regarding the heart's activity captured by V3. The left sternal border is more associated with V1 and V2 leads, while the anterior axillary line corresponds to the V5 and V6 leads which are used for lateral wall assessment. Therefore, the placement of V3 equidistant between V2 and V4 is the correct choice for optimal heart signal acquisition in that area.