Objective: To analyze the knowledge and perceptions of the nursing team about arrest and cardiopulmonary resuscitation in adults before and after in situ simulation in emergency care. Method: A sequential explanatory mixed methods study conducted in an Emergency Care Unit. Quantitative data were obtained through pre- and post-simulation questionnaire answered by 21 professionals and analyzed using descriptive and inferential statistics. The qualitative data was obtained through individual structured interviews with 19 professionals, analyzed according to thematic content analysis. The data was combined through connection. Results: In situ simulation did not significantly change pre- and post-simulation knowledge. Hand positioning for cardiac compressions and handling the automatic external defibrillator had the lowest number of correct answers. The qualitative data indicated difficulties related to knowledge, such as lack of training and insufficient experience with cardiopulmonary resuscitation. Conclusion: No statistically significant differences were identified in the proportions of answers obtained through the pre- and post-simulation in situ questionnaire regarding correct answers and wrong answers. Furthermore, the qualitative data reinforced the professionals’ lack of experience in critical situations, the lack of training and ongoing studies on the subject.