In Italian hospitals equipped with an Emergency Department (ED), it is possible that patients coming from such a structure occupy beds that had previously been scheduled for other patients. This happens because of some law regulations that give these kind of patients preferential access to hospitalization, and it may cause reduction in, or even stop, scheduled surgery activities. For such a reason operating theaters, surgery teams, sterilization structure, etc., are often unable to operate in an efficient way. Regarding costs and hospital management, this issue become considerable, and maybe even more unpleasant for patients on the waiting list since their scheduled surgery date generally is delayed by a long time. Studying an ED, the authors decided to build a System Dynamics model to analyze the impact of the admission from ED on other hospital structures, and thus identify the critical threshold. Some "non trivial" corrective actions have been evaluated in order to suggest how to address the problem which is currently causing internal conflicts and, if not managed, is destined to grow over time.