12-Lead ECG Placement Cheat Sheet (With Illustrations)

There is a huge misconception when it comes to cardiology — that your level of licensure is directly linked to your ability to understand the complexities of the heart. Sorry to disappoint all the country music singers and coffee shop philosophers out there, but the heart is not an incomprehensible mystery… it’s a muscle!

The 12-lead electrocardiogram (ECG) is widely used in both the prehospital and hospital settings to capture the electrical activity of the heart. However, before you learn how to read an ECG, its paramount that you understand how to capture an ECG. Incorrect electrode lead placement can result in a bad tracing of electrical activity and could possibly result in an inaccurate or incorrect diagnosis.

When we talk about 12-lead ECGs there are two terms that are important to differentiate. A lead is a unique look at the electrical activity of the heart. An electrode is the technological conductor that records the activity. Some use the words interchangeably, but that is not technically correct. 

There are two kinds of electrodes: limb and precordial.

Limb Leads

Limb lead electrodes were given their name for a reason. In order to get an accurate view of the different planes of the heart, these four leads must be placed on the limbs — not on the shoulders and/or abdomen. The limb leads are also the standard “cardiac monitoring” electrodes.

The four limb electrodes are labeled (RA, LA, etc…) and color coded to denote their placement.

  • RA — Right Arm (White)
  • LA — Left Arm (Black)
  • LL — Left Leg (Red)
  • RL — Right Leg (Green)

If you’re electrodes have faded or worn to the point that you can’t see the label it’s good to know the color code by heart. Two helpful mnemonics I’ve heard over the years are….

  • Smoke (black) over fire (red) and snow (white) on grass (green).
  • Salt, pepper, ketchup, lettuce. (Starting clockwise from right shoulder)

Precordial Lead Electrodes (V1-V6) — In order of how they should be placed.

  • V1 and V2 — To the right and left of the sternum in the 4th intercostal space
    • Finding the 4th intercostal space: The rib felt directly below the clavicle is the 2nd rib (the 1st rib is under the clavicle), count down to the space between the 4th and 5th rib. That is the 4th intercostal space.
  • V4 — In the 5th intercostal space on the midclavicular line.
    • Midclavicular line is halfway across the clavicle between the sternum and shoulder.
  • V3 — Diagonally between V2 and V4.
  • V6 — In the 5th intercostal space on the midaxillary line
    • Midaxillary line is in the middle of the armpit down toward the ankle
  • V5 — Split between V4 and V6

But wait. Why do we call it a 12-lead ECG when there are only 10 electrodes? Because each of the 10 electrodes looks at a the heart from a different angle and when these electrodes work together they give us a printout of 12 unique leads or “views” of the heart.