Are cardiac arrest and heart attack the same thing?                 

No, they are different, but in some cases, heart attack can lead to cardiac arrest. AED should only apply to a person who are in cardiac arrest. 

Where AED should be placed?   

All first-response vehicles should have AED, e.g. ambulances and fire engines. Also, it should be placed in public or private places where large numbers of people gather, such as shopping malls, airports and schools, or where there is reasonable likelihood of witnessed cardiac arrests. AED should be placed in visible and accessible locations, e.g. reception areas, on walls in main corridors etc. 

Who can use an AED?             

Anyone can use an AED, as long as one follows the instructions of the AED.