Cardiac disease is the most common cause of mortality in the Western World and the majority of these cardiac deaths is due to out-of-hospital cardiac arrest (OHCA). In Sweden, an estimated 5,000-10,000 people suffer an OHCA annually. The objective of this thesis is to study patient characteristics and survival in patients with OHCA, to explore the importance of pre-hospital factors and in-hospital factors and to investigate the benefits of an early defibrillation program.