Open Heart Surgery Simulation is a fascinating, interactive site from ABC's Australian Science site that makes you the surgeon performing a Coronary Artery Bypass surgery. It is simplified, but still very exciting and educational. At each step, you are provided instructions and then you must carry out the procedure. There are three different levels of difficulty and a section to just learn about the anatomy of the heart.
This is a great tool to use with Biology, Anatomy and Physiology, or medical classes.