Objective: The out-of-hospital cardiac-arrest incidence in Sweden averages about 10 000 a year. Whether the victim will survive or not is dependent upon rapid actions according to the chain of survival – early alarm, early CPR, early defibrillation and early medical treatment. While waiting for the ambulance the victim is completely dependent on immediate help from any bystander, because early CPR improves survival rates by two-three folds. Unfortunately not all bystanders start CPR because of different reasons. Aim: To describe factors influencing bystander and presumed bystanders to start cardiopulmonary resuscitation on a victim suffering from cardiac arrest out-of-hospital. Method: Literature review based on 14 scientific articles, which were reviewed and analysed. Results: Bystanders can be categorised in bystanders and presumed bystanders. The factors can be summarised in five categories, physical factors of the victim, the bystanders’ physical and psychological factors, risk of infection, legal and social factors and the bystanders’ CPR-knowledge. Conclusion: Knowledge seems to be a determining factor influencing bystanders and presumed bystanders to start CPR out-of-hospital. Through CPR-courses the nurse/CPR-instructor mentally can prepare bystanders to start CPR.