Cardiopulmonary resuscitation (CPR) and defibrillation are the interventions performed by health care professionals in order to preserve the life of a patient suffering cardiac arrest. These tasks are important to the role of nurses because they are the most common first responders to in-hospital cardiac arrest scenarios. The early initiation of CPR and defibrillation is essential in increasing the likelihood of a patient surviving cardiac arrest. Despite possessing the knowledge, skills, training, and professional obligation to deploy CPR and defibrillation independently, nurses may hesitate to perform the appropriate actions in a timely manner. This topic has been studied previously; however, there have been no studies directly examining this issue in the Ontario context. This thesis explored the factors that influence the behaviour of nurses in the first responder role by employing a mixed-methods research design. The quantitative portion of the study consisted of a series of scales on an online survey that examined teamwork factors and nurses’ experience with CPR events. The qualitative part of the study consisted of open-ended questions on the survey as well as individual interviews with nurses to understand the barriers and enablers to the role of nurses in the enactment of basic life support (BLS). The qualitative data were analyzed with a modified grounded theory approach. The qualitative data analysis followed the guidelines developed by Charmaz (2006) and employed the conceptual framework on optimizing scopes of practice developed by the Canadian Academy of Health Sciences (2014) to extrapolate findings on the influence of nurses’ scope of practice on their behaviour. This study revealed a number of contextual factors in Ontario influencing nurses’ deployment of CPR and defibrillation including variations in hospital unit types, geography, workload, the availability and quality of technology, legislation and regulation, accountability, as well as economic constraints.