You will recieve to sets of replacement pads.
The American Heart Association recommends having an extra set of pads for your AED
 
Description
Philips SMART pads, when placed on the victim’s bare skin, sense and adapt the defibrillator’s instructions to guide your actions every step of the way.
SMART pads guide the defibrillator to adapt instructions to the pace of the responder so as not to overwhelm, run ahead or slow them down. In addition to being repeated, prompts are rephrased and include additional instructions to help understanding.
SMART Analysis automatically assesses the victim’s heart rhythm and is designed to deliver therapy only if the rhythm is determined to be shockable – even if the Shock button is pressed.
With patented Quick Shock, the Heartstart AED is among the fastest in class at delivering shock treatment after CPR.
 
Compatibility with Other Philips AEDs:
These electrode pads can connect and be used with Philips HeartStart FR2, FR2+, FR3 AEDs and the Philips HeartStart MRx, XL, XLT and XL+, which are ALS defibrillators used by medical professionals. This product is compatible with most of the Philips line of AEDs, however, the electrode pads will only register as preconnected pads in the FRx and FR3 AEDs. We suggest you purchase device-specific electrode pads for the Forerunner and FR2 AEDs and all ALS defibrillators. SMART Pads II are not compatible with the HeartStart OnSite (HS1) or Forerunner AEDs.
Note: these can be converted to pediatric pads using the Philips Heartstart FRx Infant/Child/Pediatric Key, sold separately (link below). Other AED’s require you to buy separate pediatric pads every 2 years.