The study will assess 30-day survival for cases where volunteer citizen responders ('heart runners') were activated through a smartphone app to retrieve an AED in case of suspected out-of-hospital cardiac arrest (OHCA) versus standard emergency medical services care. The study will randomize emergency medical dispatch center incoming calls which are suspected out-of-hospital cardiac arrest, such that half will be randomized to activation of heart runners and half to no activation of heart runners (standard care). The study will also assess physical or psychological risks involved for the activated heart runners.