Introduction: A life threatening arrhythmia is a medical condition that requires immediate intervention, or it can cost a patient’s life. However, there is limited understanding of nurses’ knowledge and skills in identification and care provided to patients with life threatening arrhythmias in Tanzania. The objective of this study was to assess knowledge and skills of nurses in identifying life threatening arrhythmias and the required patient care. Methods: A descriptive cross-sectional study was conducted to assess the knowledge and skill level of nurses in identification of life threatening arrhythmias and the required patient care, as well as exploring the barriers in acquiring and implementing particular knowledge and skills. A convenient sample of 141 nurses working in critical care areas at Muhimbili National Hospital, were recruited. Results: The majority (44%) of the participants were 31-40 years old and more than three quarters were females. The majority (60%) scored highly when tested about their knowledge of life threatening arrhythmia identification. However, the majority of nurses (84.4%) scored poorly when being observed on their skills. A total of 116 (82.3%) nurses were able to identify asystole on an electrocardiogram strip, and demonstrated a high level of knowledge (95%) in the nursing care of patients in asystole. Although they demonstrated poor skills in general, nurses were competent (97.9%) in electrode placement on the patient’s chest before connecting the patient to the cardiac monitor. The overwhelming workload was identified by many (68.8%) as the major barrier in acquiring and implementing knowledge and skills. Conclusion: Although the majority of the participants scored highly in their level of knowledge regarding life threatening arrhythmias, they scored poorly in most of the observed skills when identifying and treating this patient group. It is important that hospital administration take into consideration the identified areas of deficiency and work to improve the skills among nurses and enhance optimal care of patients.