Definition - As its name says it is a sudden death due to a stop of heart function.
Symptoms - Death ( obviously ) , unconsciousness due to lack of blood flow.
Causes - Most deaths by this are caused from abnormal heart rhythms called arrhythmias. There can be others, but this is the most prominent reason.
Incidents - It causes about 325,000 deaths in the us a year, which is nearly half of all natural deaths.
Prevention - There aren't really any prevention, except for trying to take care of your heart. Which basically means don't drink, smoke , be active, and don't eat Mc Donalds...
Treatment - The only treatment is trying to restart the heart with an electric shock, which is not likely to happen because of the suddenness of its onset.