This thesis explored the factors that influence the behaviour of registered nurses in the first responder role by employing a mixed methods research design. In addition, this research aimed to extrapolate findings on the influence of nurses’ scope of practice on their behaviour by employing the conceptual framework on optimizing scopes of practice developed by the Canadian Academy of Health Sciences (2014) to inform a portion of the qualitative data analysis. 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; however, despite possessing the knowledge, skills, and training to initiate CPR independently, nurses may hesitate to perform these actions in a timely manner. This topic has been studied previously, but there have been no studies directly examining this issue in the Ontario context. 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.