Background: Ventricular dysrhythmias (VD) are the important cause of cardiovascular morbidity and mortality, particularly in those with structural heart disease. It is fundamental importance for nurses to recognize normal and pathological electrocardiographic tracings and allowing the adoption of appropriate and immediate interventions. Aim of the study: was to assess nurses' performance regarding life threatening ventricular dysrhythmia among critically ill patients in intensive care units at Zagazig University Hospitals. Subjects and Methods: Research design: A descriptive design was utilized to achieve the aim of this study and to answer the research questions. Setting: The study was conducted at all cardiac Intensive Care Units at Zagazig University Hospitals. Subjects: A convenient sample of 50 nurses was included in this study. Tools of data collection: Two tools were used; Questionnaire and observational checklists regarding life threatening VD. Data were collected over a period of six months started from July 2018 to December 2018. Results: The results of the study revealed that the majority of the studied nurses their age ranged from 20-29 years old and was female, near to half of nurse's graduated from bachelor nursing, and two third of nurses had years of experience in ICU more than 2 years. The present study clarified that three quarter of the studied nurses had unsatisfactory knowledge and more than half of them had unsatisfactory practice regarding life threatening ventricular dysrhythmias. Conclusion: Based on the results can be concluded that the studied nurses had unsatisfactory level of knowledge and practice regarding life threatening VD and need to be improved. Also, there was no significant relation between total knowledge score and total practice score. Recommendations: the study is recommended to there is a need to In–service training programs for the purpose of updating the knowledge and skills of nurses working with intensive care units for early identification and management of life threatening dysrhythmias and Periodic evaluation of nurses' knowledge and practice.