Resuscitation from clinical cardiac arrest is complex and often takes several years to learn. This paper describes an intelligent simulation-based tutor for ACLS which increases students' opportunity to practice before, during and after the ACLS course, thus bridging the gap between studying theory and didactic textbook material and working with patients. Sophisticated reasoning about student performance, compared to an expert model, distinguishes this system from other computerized instruction systems. Intelligence in the tutor allows the system to make the simulation dynamically adaptive to focus on areas where the student's learning needs are greatest. A formative evaluation with two classes of fourth year medical students suggested that the tutor was helpful, realistic and effective. Positive reactions and strong student involvement with the simulation suggest that this simulation-based tutor may improve learning and retention while decreasing anxiety for most students.