Defibrillator pads are placed in two positions on the bare chest: one below the right collarbone, just to the right of the breastbone, and the other on the left side of the torso, below the armpit along the mid-axillary line. This standard layout is called anterolateral placement, and it’s what most AED diagrams printed on the pads themselves will show you.
Standard Anterolateral Placement
The goal is to position the two pads so the electrical current travels directly through the heart. The upper right pad goes just below the collarbone, slightly to the right of the sternum (the flat bone running down the center of the chest). The lower left pad sits on the side of the ribcage, roughly below the left armpit at about the level of the nipple. Most AED pads have printed diagrams showing exactly where each one goes, and the pads are often labeled “upper right” and “lower left” to eliminate guesswork.
This anterolateral position is recommended by the American Red Cross as the default because it’s fast to apply and keeps you out of the way of chest compressions. You don’t need to roll the person over or reposition them, which saves critical seconds during cardiac arrest.
Why Placement Matters
Defibrillation works by passing enough electrical current through the heart to reset its rhythm. The pads need to bracket the heart so the current flows through the maximum amount of cardiac tissue. If pads are too close together, too high, or placed over bone instead of soft tissue, the current may not reach enough of the heart to be effective.
Several factors affect how well the electrical current penetrates the chest wall. These include the size of the person’s chest, how firmly the pads are pressed against the skin, and whether there’s good contact between the pad and the skin surface. Poor contact from moisture, chest hair, or air gaps under the pad increases resistance and reduces the shock’s effectiveness.
Anteroposterior Placement
An alternative layout places one pad on the center of the chest (over the breastbone) and the other on the back, between the shoulder blades. This is called anteroposterior placement. You’ll sometimes see it used in hospital settings or for certain heart rhythm problems like atrial fibrillation.
A meta-analysis of randomized controlled trials found no significant difference in shock success between anteroposterior and anterolateral positioning overall. Neither first-shock success nor overall success rates were meaningfully different. However, subgroup analysis suggested that for older patients, those with a higher BMI, or those who had been in atrial fibrillation for a longer period, the standard anterolateral position may actually work slightly better with modern biphasic defibrillators.
For bystander use of a public AED during sudden cardiac arrest, anterolateral is the standard. Anteroposterior placement requires rolling the person, which interrupts CPR and costs time.
Placement on Women
On female patients, the lower left pad should go lateral to or underneath the left breast, not directly on top of breast tissue. Research published in the Journal of the American College of Cardiology found that placing the pad on the breast increases the electrical resistance of the chest wall, reducing current flow to the heart. Lift or move the breast to the side if needed, and press the pad firmly against the ribcage beneath it. The upper right pad placement stays the same, below the right collarbone.
Placement on Children
For children under 8 years old (roughly under 25 kg or 55 pounds), use pediatric pads if the AED kit includes them. These pads deliver a lower energy dose. If only adult pads are available, use those instead, as delivering a shock with adult pads is better than not defibrillating at all.
On small children, the two pads may be too large to fit on the chest without touching each other. In that case, use anterior-posterior placement: one pad on the center of the chest, one on the center of the back. Studies have found no significant difference in the AED’s ability to analyze heart rhythms between sternal-apical and anterior-posterior positions in children, so either layout works. The key is making sure the pads don’t overlap.
Preparing the Chest Before Placement
The pads need direct contact with bare, dry skin. Before placing them, you may need to address a few common obstacles.
- Chest hair: Thick hair prevents the pads from adhering properly. Most AED kits include a small disposable razor. Quickly shave the two pad areas before applying them. If the hair is sparse or fine, modern pads will usually stick well enough without shaving. If no razor is available, press the pads down as firmly as you can.
- Wet skin: Wipe the chest dry with a towel or clothing before applying pads. If the person is lying in a puddle, move them to a dry surface first. Water on the skin can cause the electrical current to travel across the surface of the chest rather than through it.
- Medication patches: If you see a transdermal patch (nitroglycerin, nicotine, hormone patches) in the area where a pad needs to go, peel it off and wipe the skin clean before placing the pad. The patch can block contact and in some cases cause a small burn during the shock.
- Implanted devices: If you notice a visible lump under the skin near the collarbone, that’s likely a pacemaker or implanted defibrillator. Place the pad at least an inch (2 to 3 cm) away from it. The standard pad positions usually accomplish this naturally, but if the device is on the right side, shift the upper pad slightly to avoid placing it directly over the lump.
Common Placement Mistakes
The most frequent errors are placing pads too close together, placing them too high on the chest, or failing to get good skin contact. Pads placed side by side on the front of the chest instead of in the correct upper-right and lower-left positions will short-circuit the current across the surface rather than driving it through the heart.
Another common mistake is placing pads over clothing, jewelry, or underwire bras. All clothing needs to be removed from the chest area. If you can’t unclasp or remove a bra quickly, cut it. Speed matters, but so does direct skin contact. An AED that analyzes the rhythm and delivers a shock through fabric or metal may misread the heart’s electrical activity or deliver an ineffective shock.
Don’t hesitate to reposition pads if the AED gives a “check pads” error message. That warning almost always means one or both pads aren’t making solid contact with the skin. Press them down firmly, or peel and reapply if the adhesive has picked up moisture or hair.