HeartStart HS1 Defibrillator* Event Registry

Inclusion Criteria:

* Have been suspected of a circulatory arrest for any cause.
* Have had HeartStart HS1 Defibrillator with electrodes:

Adult SMART Pads Cartridge \[REF: M5071A\], Infant/Child SMART Pads Cartridge (REF:M5072A) applied to their body and powered up with HS1 battery (Model M5070A), regardless of whether a defibrillation shock was delivered

Exclusion Criteria:

* Subjects will be excluded if any of the following are present:
* AED or pad use other than the HeartStart HS1 Defibrillator with above referenced Philips electrode pads. Note: Use of a device other than the Philips HeartStart HS1 AED does not preclude enrollment if the AED or an Advanced Life Support defibrillator was used after the HeartStart HS1 AED.
* AED used for training purposes.