Anterior/posterior placement on an infant means one AED pad goes on the front of the chest, centered over the heart area (the anterior position), and the second pad goes on the infant's back, directly behind the first pad (the posterior position). The pads end up facing each other with the heart between them. That's the whole answer. Everything else in this article covers how to actually get them there on a small body, which pad goes where, what to do when a back isn't accessible, and where this placement sits relative to the other AED options for infants.
The short version matters because infant AED use happens under pressure. A rescuer has seconds, not minutes, and the pad placement decision is one of the few things they fully control.
What Anterior/Posterior Means on an Infant and Why the Heart Sits Between the Pads
Anterior means front, posterior means back, and the pairing puts the heart in the path between two electrodes. On an infant, that path is short. A newborn's chest is roughly the size of an adult palm, and the heart sits close to the front chest wall, so the electrical vector between front and back runs across a small distance with little tissue to cross.
Defibrillation works by sending current through the myocardium. Pad position determines the direction and density of that current. When one pad sits on the sternum and the other on the back, the current enters the front of the chest and exits through the back, passing through the heart on the way. That's the physical reason this arrangement shows up in infant guidance.
The anterior/posterior arrangement is one of several positions taught for defibrillation. The others include anterior/anterior (both pads on the front of the chest), anterior/lateral (front and side), and anterior/axillary (front and under the arm). Each creates a different current path. For infants, the front-and-back layout is commonly recommended because a small torso leaves little room to separate two front pads without them touching.
Size drives the decision. Adult pads are typically around 8 to 13 cm across depending on the manufacturer, while infant pads are smaller, often in the 4.5 to 5.5 cm range. On a 5 kg infant, two adult pads placed front-to-front frequently touch or overlap. Touching pads create a short circuit, and the current never crosses the heart. Front-and-back placement solves that geometry problem by putting distance between the electrodes.
How to Place the Pads, Step by Step, in the Order You Actually Do It
Get the sequence right and the rest is manageable. The steps below assume the AED is already on and the rescuer is following the device's voice prompts. AED prompts will sometimes name pad positions differently, so read the package and listen to the device before applying anything.
1: Dry the chest and back. Wipe away moisture, sweat, or pooled water with a cloth or gauze. Wet skin lets current travel across the surface instead of through the heart, and pads don't adhere to wet skin. 2: Remove clothing and any medication patches from both the front of the chest and the upper back. Nitroglycerin, nicotine, and pain patches can block current or cause burns. Chest hair on an infant is usually not a factor, but wipe away any residue. 3: Peel the first pad and place it on the front of the chest, centered over the sternum, just below the collarbone line and above the nipple line. Press firmly from the center outward so the adhesive contacts skin across its full surface. 4: Peel the second pad and place it on the back, centered directly behind the front pad, between the shoulder blades. On a small infant, the pad may cover much of the upper back. Press it down the same way. 5: Check for contact between the pads. Look along both sides of the torso. The front and back pads should not touch at the armpits or along the sides. If they do, reposition one pad toward the center of its surface. 6: Connect the pads to the AED if the device uses a separate connector, then clear everyone away and let the device analyze. 7: Follow the AED's prompts for the shock, and resume CPR immediately after any shock or if no shock is advised.
When something fails, the fix usually involves adhesion or contact. If a pad lifts at an edge, press it back down; if it won't stick because the skin is wet or oily, dry the area again and replace the pad with a fresh one rather than taping it. If the AED reports "check pads" or "poor pad contact," press both pads firmly and check the connector before replacing them. Never cut or trim a pad to make it fit, since that can expose the conductive gel and create a bridge between electrodes.
Which Pad Goes in Front and Which Goes on the Back
The front pad goes on the chest, and the back pad goes behind it. That's the standard reading of anterior/posterior, and it matches how defibrillation current is meant to travel. The labels on some pads say "sternum" and "apex," which are terms borrowed from adult anterior/anterior placement, not front/back placement. On infant pads, look for a front/back label or a diagram, and when the packaging is ambiguous, place the pad marked for the sternum on the chest.
The two pads are functionally identical electrodes. What differs is their position, not their electronics. Some manufacturers print a diagram on the pad backing showing the intended layout. Follow that diagram when it exists, since the maker's diagram is the authoritative placement guide for that specific pad.
If the pads are already connected to the AED by a shared cable, orientation still doesn't matter electrically. What matters is that one pad is on the front and the other on the back, with no skin-to-skin contact between them.
Where Exactly on the Chest and Back Do the Pads Go
On the chest, center the pad on the sternum, roughly midway between the collarbones and the bottom of the rib cage. The pad should sit over the heart, which on an infant is closer to the midline than on an adult. Avoid the nipple itself, since the pad adhesive works better on flat sternal skin, and avoid the lower tip of the sternum where the rib cage narrows.
On the back, center the pad between the shoulder blades, at the same height as the front pad. Aligning the two pads vertically keeps the current path straight through the heart. If the back pad drifts low toward the waist or high toward the neck, the current vector tilts and some of the energy misses the target.
Avoid bony prominences and the spine itself. A pad sitting directly on the spine still works, but the bony ridge can lift the adhesive at its edges and reduce contact. Place the pad slightly to either side if the spine creates a raised ridge under the center.
Keep both pads clear of the infant's neck and airway. On a very small infant, the front pad can extend up toward the collarbone, and the rescuer should check that it doesn't ride up onto the throat or interfere with a bag-valve mask seal.
What to Do When You Can't Reach the Infant's Back
Sometimes the back isn't available. The infant may be in a car seat, strapped to a backboard, lying in a confined space, or positioned in a way that makes turning them over unsafe or impractical. In those cases, rescuers need a fallback.
The common fallback is anterior/anterior placement, with one pad on the front of the chest and the second pad on the front as well, separated as far as the torso allows. On a small infant, front-to-front placement risks the pads touching, so the two pads need to be squeezed into the available space without overlap. Some guidance for infant AED use describes placing one pad on the front and the other on the back when possible, with front-to-front as an alternative when the back can't be reached.
Another fallback is anterior/lateral or anterior/axillary, with one pad on the front and the second under the arm or on the side of the chest. On infants, this is harder because the side of the chest is small and the pad often wraps onto the back anyway.
When the back can't be reached, don't force it. Use the alternative the AED's manufacturer documents, and if the device's prompts or packaging specify a placement for small patients, follow them. The rescuer's job is to get two pads onto the infant without them touching and with the heart between them, and the front/back layout is the cleanest way to do that when the body allows.
When to Use Infant Pads Instead of Adult Pads on a Small Body
Infant pads exist because adult pads are too large for small bodies. The general rule in AED guidance is to use pediatric pads or a pediatric attenuator for children under 8 years old or under about 25 kg (55 lb), and to use adult pads if pediatric pads aren't available. The attenuator reduces the energy delivered so a small body doesn't receive an adult-sized dose.
Some AEDs ship with pediatric pads, some have a pediatric key or switch, and some only have adult pads. Check what the device carries before an emergency, because the difference between an attenuator and a full-energy shock matters for a small patient. If only adult pads are on hand, place them in the anterior/posterior arrangement so they don't touch, and deliver the shock as the device directs.
| Pad type | Typical pad size | Intended patient | Placement on an infant |
|---|---|---|---|
| Infant/pediatric pads | About 4.5β5.5 cm | Under 8 years or under 25 kg | Anterior/posterior, front and back |
| Adult pads with pediatric attenuator | About 8β13 cm | Under 8 years or under 25 kg, with reduced energy | Anterior/posterior to avoid pad contact |
| Adult pads, no attenuator | About 8β13 cm | Any age when pediatric options are unavailable | Anterior/posterior, pads kept apart |
Pad dimensions vary by manufacturer, so confirm the exact size on the package rather than relying on a general figure. The pattern is consistent though: smaller pads for smaller bodies, and front/back placement to keep whichever pads you have from touching.
Why Pad Contact Fails on Infants and How Rescuers Fix It
Pad contact fails on infants more often than on adults, and the reasons are physical. An infant's torso is small, curved, and often damp. The chest wall moves with every breath, and a crying infant shifts the skin under the adhesive. Pads that sit well on an adult chest can lift at the corners on an infant within seconds.
The most common failure is edge lift from moisture or movement. The fix is to dry the skin thoroughly before applying, press the pad from the center outward, and smooth the edges down. If a pad still lifts, press it back into place; if it won't stay, replace it.
The second failure is pad-to-pad contact. On a small infant, front pads placed too far apart or too close to the sides can touch at the armpits. The fix is anterior/posterior placement, which puts the pads on opposite sides of the body where they can't meet.
The third failure is a poor connection at the cable. Infant pads sometimes use a different connector than adult pads, and a pad plugged into the wrong port won't register. Check that the connector clicks into the AED's pad port, and if the device reports a pad fault, reseat the connector before replacing the pads.
Infant AED Placement vs. Adult and Child Placement: A Side-by-Side Comparison
Placement logic changes with body size. An adult torso has room for two pads on the front, and anterior/anterior or anterior/lateral placement works. A child's torso is smaller but often still fits front pads. An infant's torso is small enough that front pads frequently conflict.
| Factor | Adult | Child (1β8 years) | Infant (under 1 year) |
|---|---|---|---|
| Typical pad choice | Adult pads | Pediatric pads or adult pads with attenuator | Infant pads or adult pads with attenuator |
| Common placement | Anterior/anterior or anterior/lateral | Anterior/anterior or anterior/posterior | Anterior/posterior |
| Risk of pad contact | Low | Moderate | High with front-to-front placement |
| Main placement challenge | Chest hair, moisture | Pad size relative to torso | Small torso, pad contact, back access |
| Fallback if back is unreachable | Not usually needed | Anterior/anterior | Anterior/anterior or manufacturer's alternative |
The table makes the infant row stand out. The main challenge isn't getting the pads on; it's getting them on without touching and with the heart between them. Anterior/posterior placement handles both.
Common Mistakes That Undermine Front-and-Back Pad Placement
The mistakes below show up repeatedly in training and in real resuscitations. Each one has a concrete fix.
Placing both pads on the front because the rescuer is used to adult placement. On an infant, this risks pad contact. Fix: turn the infant to reach the back, or use the manufacturer's alternative. Putting the back pad too low, near the waist. The current path tilts downward and misses part of the heart. Fix: align the back pad with the front pad at the shoulder-blade level. Leaving the chest wet after wiping. Moisture bridges the pads and reduces current through the heart. Fix: dry thoroughly, then apply. Cutting a pad to fit. Trimming exposes conductive gel and can bridge the electrodes. Fix: use the correct pad size or reposition. Forgetting to remove medication patches. Patches block current and can burn. Fix: check the chest and back before applying pads. Pressing the pads only in the center. The edges lift first. Fix: press from the center outward and smooth the edges. Resuming CPR late after a shock. Every second off the chest reduces the chance of a good outcome. Fix: resume compressions immediately after the shock or the no-shock advisory.
Each mistake has a simple correction, and the corrections are what a rescuer can rehearse before an emergency rather than improvise during one.
How Infant Anatomy Changes What "Good Placement" Looks Like
An infant's chest is not a scaled-down adult chest. The rib cage is more cartilaginous, the sternum is shorter, and the heart sits higher and more midline. The liver is proportionally larger and sits close to the lower rib cage, which matters because current that exits low on the torso can pass through the liver rather than the heart.
That anatomy explains why the front pad sits relatively high on the sternum and the back pad sits at shoulder-blade level. Both positions keep the current path through the heart and away from the liver and stomach. A pad placed low on the front of the chest, near the bottom of the rib cage, sends current through the abdomen on its way to the back.
The infant's small size also means the pads cover a larger fraction of the torso than adult pads do on an adult. On a 5 kg infant, an infant pad can cover much of the front chest wall. That's fine as long as the pad doesn't touch the other pad or ride up onto the neck, and it's another reason front/back placement is preferred: it keeps each pad on its own surface.
Body position matters too. An infant lying flat on a firm surface is easiest to place pads on, and turning the infant to reach the back is a two-person job when possible. If only one rescuer is present, the rescuer turns the infant, places the back pad, turns the infant back, and places the front pad, keeping the infant's airway open throughout.
FAQ
Can you use adult pads on an infant in anterior/posterior placement?
Yes, when infant pads aren't available. Adult pads are larger, so the front and back positions are the ones that keep them from touching. Place one on the chest and one on the back, press firmly, and follow the AED's prompts. The energy delivered will be adult-sized unless the device has a pediatric attenuator, which is why checking the AED's pad inventory before an emergency matters.
Do the two pads have to be exactly opposite each other?
They should be roughly aligned, with the back pad centered behind the front pad. Exact alignment isn't possible on a moving infant, but a back pad that sits several centimeters off-center tilts the current path. Aim for the same height on both sides: sternum on the front, between the shoulder blades on the back. Small offsets are acceptable; large ones are not.
What if the infant is too small for two pads to fit without touching?
That's the situation anterior/posterior placement is designed for. Putting the pads on opposite sides of the body gives them the most separation available. If even that leaves the pads touching at the sides, reposition each pad toward the center of its surface, and check the pad packaging for the manufacturer's guidance on small patients.
Is anterior/posterior placement the same as anterior/lateral?
No. Anterior/posterior puts one pad on the front and one on the back. Anterior/lateral puts one pad on the front and one on the side of the chest, often under the arm. On infants, the side of the chest is small, so an anterior/lateral pad often wraps onto the back anyway. The two positions produce different current paths, and the front/back layout is the one commonly recommended for infants.
What happens if the pads touch each other?
The current takes the short path between the pads instead of crossing the heart, so the shock doesn't do what it's supposed to do. The AED may also report a pad fault or refuse to analyze. If the pads touch, separate them by repositioning, or switch to front/back placement if they were both on the front.
Should the front pad go above or below the nipple line?
Center the front pad on the sternum, generally above the nipple line and below the collarbones. On an infant, the heart sits high and midline, so a pad centered on the upper sternum puts current through the heart. A pad placed low on the chest sends current toward the abdomen.
Can I place the pads while the infant is being carried?
Not safely. Pad placement requires a still, dry surface and firm contact, and a moving infant makes both impossible. Place the infant on a firm, flat surface first, dry the skin, then apply the pads. If the infant must be moved, place the pads afterward, not during.
Do I need to shave the infant's chest before placing pads?
Chest hair is rarely a factor on an infant, so shaving isn't part of infant pad placement. What matters is dry skin, no medication patches, and firm adhesion. If a patch or residue is present, wipe it away before applying the pad.
This article is general educational information about AED pad placement and is not a diagnosis, treatment plan, or substitute for certified CPR and first aid training. Pad placement guidance varies by manufacturer, and the device's own prompts and packaging are authoritative for the model you have. For any actual emergency, call your local emergency number immediately and follow the directions of trained dispatchers and responders; if you or someone else is in crisis or at risk of self-harm, contact local emergency or crisis services.