Enhancing competency and collaboration has become a salient topic of the professional debate on medical safety issues. The advantages of simulation-based training scenarios for team communication, routines and critical work procedures especially in operation theatres have been vigorously discussed. However, the literature on simulation-based training theorises the respective learning mainly as a form of practising technical and non-technical skills and, thus, provides an insufficient understanding for several risks connected to simulations such as confirming a false feeling of safety or over-routinising procedures. Such problems of simulation-based learning can only be prevented or converted into strengths by developing a profound understanding of the specific knowledge-in-practice and the "scientification of work" which it implies. Against the background of a study on simulation-based trainings for perfusionists at the German Heart Institute (Berlin), this article elaborates an expanded understanding of "work process knowledge" and connects theoretically to Bengt Molander who compares knowledge to a form of "attentiveness" and "presence". The study shows that this knowledge-in-practice grounds in different activities to co-construct and collectively frame the object and the task of work. The quality of these activities depends not only on skills in communication but also on the socio-material enactment of professional roles.