The preferred pad placement for an adult AED is the anterolateral position: one pad on the upper right chest below the collarbone, and the second pad on the lower left side of the chest beneath the armpit. This configuration sends the electrical shock across the heart from one side to the other, giving the best chance of restoring a normal rhythm.
Anterolateral Placement Step by Step
Anterolateral placement is the default position taught in CPR and first aid courses, and it’s what the diagrams printed on AED pads illustrate. The right pad goes on the upper right chest, just below the collarbone and to the right of the breastbone. The left pad goes on the lower left side of the ribcage, a few inches below the armpit. Together, the two pads create an electrical pathway that passes directly through the heart.
This positioning works because defibrillation delivers energy in joules from one pad to the other, creating a current across the chest. The success of that shock depends on how well the current path encompasses the heart. Anterolateral placement lines up the pads so the shock travels through the largest possible cross-section of cardiac tissue.
Anteroposterior Placement as a Backup
If anterolateral placement isn’t feasible, for example because of a chest wound, a device, or body shape, the anteroposterior position is the recommended alternative. One pad goes on the front left chest, centered between the midline of the chest and the nipple. The second pad goes on the back, on the left side of the spine just below the shoulder blade.
For female patients, the American Red Cross recommends placing the front pad to the left of the lower breastbone, positioning it to avoid breast tissue as much as possible. The back pad stays in the same spot, on the left side of the spine below the shoulder blade.
This front-and-back configuration is also used in hospital settings when a patient’s heart rhythm isn’t responding to repeated shocks. After three unsuccessful defibrillations, trained healthcare providers may switch from anterolateral to anteroposterior placement to change the direction of the electrical current through the heart.
Preparing the Chest Before Placing Pads
AED pads need direct contact with bare, dry skin to work properly. Before placing them, you may need to address a few obstacles.
- Wet skin. If the person was pulled from water or is sweating heavily, dry the chest with a towel or clothing before applying pads. Never use an AED while a person is submerged in water. Move them to a dry surface first.
- Excessive chest hair. The pads must stick firmly to the skin. If thick chest hair prevents good adhesion, shave the areas where the pads will go. Most AED kits include a disposable razor for this purpose.
- Medication patches. Remove any transdermal patches (nitroglycerin, nicotine, hormone replacement, pain medication) from the chest and wipe the area clean before attaching a pad. A patch left in place can block energy delivery and cause small skin burns.
- Implanted devices. If you see or feel a hard lump under the skin of the upper chest, that’s likely a pacemaker or implanted defibrillator. Place the AED pad at least four finger-widths away from it rather than directly on top.
Adult Pads vs. Pediatric Pads
Standard adult AED pads are designed for anyone roughly eight years old or older, or over 55 pounds. Pediatric pads deliver a lower dose of energy and should be used for children under eight or under 55 pounds. If pediatric pads aren’t available, adult pads can be used on a child, but make sure the two pads don’t touch each other on the smaller chest. Some AED models have a switch that reduces the energy output to a pediatric dose.
The reverse is not true: pediatric pads should never be used on an adult. They don’t deliver enough energy to defibrillate an adult heart effectively.
Why Pad Contact Matters
The biggest source of electrical resistance during defibrillation is the interface between the pad and the skin. Air gaps from poor adhesion, moisture, hair, or patches all reduce the current that actually reaches the heart. Pressing the pads firmly onto clean, dry skin makes a meaningful difference in whether the shock works. Some advanced protocols even call for applying manual pressure to the pads during shock delivery to improve contact, though that’s primarily a technique for trained medical teams with insulated gloves.
If you’re using an AED for the first time, follow the pictures printed on the pads and the voice prompts from the device. AEDs are specifically designed so that someone with no medical training can use them correctly. Getting the pads in roughly the right position, with good skin contact, is far more important than achieving millimeter-perfect placement.