New-onset postoperative atrial fibrillation (POAF) is a common complication after cardiac surgery, with an incidence rate of 20-60%. It is associated with increased perioperative morbidity, mortality, and healthcare costs. In addition, it is an independent predictor of early and long-term cardiovascular complications. The primary objective of this study was to construct a predictive model for assessing the development of POAF after isolated aortic valve replacement (AVR) based on clinical and procedural parameters. The secondary objective was to determine the incidence of POAF. A retrospective cohort study was conducted, including all consecutive patients undergoing isolated AVR from January 2010 to December 2022 at the Clinic for Cardiac Surgery of the University Hospital Center Zagreb. The study found a prevalence rate of POAF of 26.8%. The final model of multivariate analysis identified age (p<0.001), length of stay in the intensive care unit (p=0.001), and mechanical ventilation (p=0.023) as significant risk factors for the development of POAF after isolated AVR. The simple predictive model developed in this study is a valuable tool for identifying patients at high risk of developing POAF after isolated AVR. Implementation of targeted interventions based on risk assessment could lead to better outcomes and reduced healthcare costs.