Objective: to analyze nurses' knowledge and practices regarding the care provided to patients in cardiopulmonary arrest in the emergency room of a medium and high complexity public hospital in Belém, State of Pará, Brazil. Method: this descriptive, exploratory, qualitative study included ten nurses, who work in the urgency and emergency service. Data collection took place from February to March 2019 through semi-structured interviews. Thematic content analysis proposed by Bardin was used to construct the data. Results: the studied population has deficient and sometimes insufficient knowledge, mostly marked by mistaken speeches and uncertainties, revealing gaps in knowledge and divergences in relation to the resuscitation science consensus necessary to perform adequate care during a cardiorespiratory arrest, and may compromise the effectiveness of cardiopulmonary resuscitation, causing damage to resuscitation and, consequently, contribute to the emergence and / or aggravation of sequelae, which can impact on increased morbidity and mortality. Conclusion: knowledge deficiency is multifactorial, which may be related to the lack of continuous and permanent education, and the lack of personal motivation for the constant search for knowledge, in addition to the lack of incentive to update proposed by the head of the service in the studied scenario.