The assessment of nursing workload offers both support for patient care planning and service management. In an Intensive Care Unit (ICU) this workload is measured by the Nursing Activities Scores (NAS), although in specialized areas such as Cardiology, its use is still diminished. Objective: To describe NAS and the prevalence of its sub-items in a Brazilian Cardiac ICU. We also aimed to evaluate NAS oscillation since the opening of the unit, and according to the day of the week. Methods: Daily NAS records collected from November 2014 to October 2018 were assessed, totaling 8600 assessments distributed over 49 months. The data were analyzed according to time, day of the week, number of records per day, and dichotomizing if NAS was higher or lower than 50 points. Results: NAS presented mean value of 52.91 points and a median of 53.40 points. The mean NAS values per month ranged from 45.00 to 59.10 points. The percentage of NAS assessments above 50 points ranged from 20.59 to 92.34% per month and proved to be a better indicator for assessing the variability of the monthly workload. When combined two by two, 66.01% of NAS combinations scored more than 100 points, suggesting the need for more than one nursing professional per day. When the data were stratified by year, 2018 had the lowest means compared to the others. When compared to the mean values in function of the day of the week, it was observed that Monday to Friday (with the highest mean on Wednesday, the predominant day for cardiac surgeries) showed higher values than weekends. Conclusions: Overall, NAS showed low values compared to other general or cardiac ICUs, it also presented temporal variability and our results showed risk of workload overload which can compromise patient care and safety. Such results reinforce the importance of the administrative and assistant aspects of the routine use of NAS in ICUs specially in specialized environments as Cardiac ICU.