Which color lead is used for the positive electrode in a three lead system?

In a three-lead ECG system, the positive electrode is designated by the color red, typically associated with the left leg (LL) in standard conventions. The purpose of the positive electrode is to capture electrical signals from the heart and provide a reference point for recording the electrical activity. Since the left leg usually serves as the ground reference in many setups, the red lead effectively captures the heart's electrical signals relative to the other electrodes.

The other colors have specific roles as well: white is used for the right arm (RA), black represents the left arm (LA), and green is used for the right leg (RL) in a standard three-lead setup. However, none of these alternatives serve as the designated positive electrode in this configuration, which is why the recognition of red as the positive lead is essential for accurate ECG interpretation and monitoring.