ECG Leads
Learn about each ECG lead. Electrode placement, normal findings, and clinical interpretation for the standard 12-lead ECG.
Limb Lead I
Lead I is a bipolar limb lead that measures the electrical potential difference between the left arm (positive) and the right arm (negative), recording lateral left ventricular activity along a 0-degree axis.
limbLimb Lead II
Lead II is a bipolar limb lead measuring the electrical potential difference between the left leg (positive) and the right arm (negative), oriented at +60 degrees and aligned closely with the normal cardiac axis, making it the most commonly used rhythm monitoring lead.
limbLimb Lead III
Lead III is a bipolar limb lead measuring the electrical potential difference between the left leg (positive) and the left arm (negative), oriented at +120 degrees in the frontal plane and providing a rightward inferior view of cardiac electrical activity.
limbAugmented Lead aVR
Lead aVR is a unipolar augmented limb lead oriented at -150 degrees (or equivalently +210 degrees), recording from the right arm and pointing away from the cardiac apex. It provides a unique 'right shoulder' perspective of cardiac electrical activity, viewing the heart from above and to the right.
augmentedAugmented Lead aVL
Lead aVL is a unipolar augmented limb lead oriented at -30 degrees in the frontal plane, recording from the left arm and providing a high lateral view of the left ventricle. It is a crucial lead for detecting high lateral myocardial infarction and evaluating left axis deviation.
augmentedAugmented Lead aVF
Lead aVF is a unipolar augmented limb lead oriented at +90 degrees, recording from the left foot and providing a direct inferior view of the left ventricle. It is a central lead in both inferior MI diagnosis and electrical axis determination.
augmentedPrecordial Lead V1
Lead V1 is a unipolar precordial lead placed at the right sternal border in the fourth intercostal space, providing a direct rightward septal view of the heart. It is among the most diagnostically versatile leads on the 12-lead ECG.
precordialPrecordial Lead V2
Lead V2 is a unipolar precordial lead placed at the left sternal border in the fourth intercostal space, providing a septal and right ventricular view. It is a critical transition lead between the rightward-facing V1 and the increasingly leftward-facing chest leads.
precordialPrecordial Lead V3
Lead V3 is a unipolar precordial lead placed between V2 and V4 on the anterior chest wall, representing a transitional zone between right-facing and left-facing precordial leads and corresponding to anterior left ventricular and septal myocardium.
precordialPrecordial Lead V4
Lead V4 is a unipolar precordial lead placed at the cardiac apex in the fifth intercostal space along the midclavicular line, providing a direct apical view of the left ventricle and serving as the reference point from which V5 and V6 are placed.
precordialPrecordial Lead V5
Lead V5 is a unipolar precordial lead placed at the anterior axillary line at the same horizontal level as V4, providing a lateral left ventricular view and generating some of the largest R-wave voltages in the standard 12-lead ECG.
precordialPrecordial Lead V6
Lead V6 is the most lateral unipolar precordial lead, placed at the midaxillary line at the same horizontal level as V4 and V5. It provides a lateral left ventricular view nearly parallel to Lead I, and serves as the final lead in the standard precordial sequence.
precordialLimb Leads Overview
The limb leads consist of six leads derived from electrodes placed on the arms and legs: three bipolar standard leads (I, II, III) and three unipolar augmented leads (aVR, aVL, aVF). Together, they survey cardiac electrical activity in the frontal plane and are essential for axis determination, rhythm analysis, and inferior and lateral wall assessment.
overviewPrecordial Leads Overview
The six precordial leads (V1–V6) are unipolar electrodes placed directly on the anterior and lateral chest wall, providing a horizontal plane view of cardiac electrical activity. They are essential for evaluating anterior, septal, lateral, and posterior left ventricular function, R-wave progression, and bundle branch block morphology.
overview