Which electrode is positioned in the mid-clavicular line on the left?

The electrode that is positioned in the mid-clavicular line on the left is V4. This electrode is placed at the fifth intercostal space, specifically in the left mid-clavicular line, which is a key position for monitoring the heart's electrical activity in electrocardiogram (ECG) assessments. The placement of V4 allows for optimal visualization of the electrical changes occurring in the heart, particularly in the left ventricle, which is critical for diagnosing various cardiac conditions.

In the context of the other electrodes, V2 is located at the left sternal border of the second intercostal space, V3 is positioned between V2 and V4, and V5 is located at the anterior axillary line at the same level as V4. These different placements serve distinct purposes in obtaining a comprehensive view of the heart's electrical activity, but V4's specific placement along the mid-clavicular line is crucial for its role in clinical practice.