The importance of bystander cardiopulmonary resuscitation (CPR) prior to arrival of the emergency medical service is well documented. In Sweden, CPR is initiated prior to emergency medical services (EMS) arrival in about 30% of cardiac arrests out-of-hospital, a figure which should be improved urgently. To do so, it is of interest to know more about the bystanders' perceptions of their intervention. A qualitative method inspired by the phenomenographic approach was applied to 19 bystanders who had performed CPR. In the analysis, five main categories and 14 subcategories emerged. The main categories were: to have a sense of humanity, to have competence, to feel an obligation, to have courage and to feel exposed. Interviews described how humanity and concern for another human being were the foundation of their intervention. CPR training offers the possibility to give appropriate help in this emergency. If the aim of CPR training was extended beyond teaching the skill of CPR to include preparation of the rescuer for the intervention and his/her reactions, this might increase the number of people able to take action in the cardiac arrest situation.