The ambulance care setting is complex and unpredictable and the personnel must prepare for upcoming assignments. Prehospital emergency care nurses (PENs), are frequently exposed to critical incidents (CIs). There are, to our knowledge, no prior studies describing experiences of requirements for management of caring for a patient during a CI in the ambulance care context. Therefore, the aim of the study was to explore PENs' experiences of care in CIs. A qualitative research design with content analysis has been used, based on semi-structured interviews with eleven PENs in Sweden. PENs' experiences can be described as: "In a critical incident, personal ability based on experiential knowledge is central to patient care". Three generic categories underpinned the main category: "Clinical expertise", "Professional approach" and "Broad knowledge base". The care given during a CI in the ambulance care setting depends on PENs' personal ability based on experiential knowledge. Employers need to build an organization providing prerequisites and support during an CI. Suggested activities are to create forums for PENs to share experiences with each other, possibility to get feedback on completed assignments and continued training to develop new knowledge and be prepared for the unpredictable environment that characterizes CI.