Moderately challenging, but immensely rewarding.

Materials:
-Upholstery foam
-1/4" PVC pipe
-Sheet steel
-Duct Tape
-Hot glue
-Ping Pong balls
-Red latex paint
-Glad Press and Seal
-Vaseline
-Picture of Open Heart Surgery for Dummies
-Old Tee shirt
-Surgical gown, mask, gloves, and hairnet (just ask local hospital or friends who work in a medical field)
-Hemostatic forceps (fishing section of sporting goods store, hardware store, Radio Shack)

I started with building the retractor (the big metal thing) by cutting out some thin sheet metal and folding it over. Then, I used upholstery foam to make a chest cavity. This was done by hollowing out an 8" by 10" depression. Then, to add structural support and to look like a cracked sternum (breastbone), I cut two 10" lengths of narrow PVC pipe and embedded them into the foam along the lateral margins of the depression. After this, I constructed a heart made of table tennis balls, plastic tubing, and duct tape, all wrapped in Glad Press and Seal wrap. Next, I painted everything red and hot glued the heart into the depression. I then added another layer of Press and Seal, this time with a cut in it, to act as a pericardial sack. Then, I cut a rectangular hole in the surgical gown fitting the size of the depression. Following this, I duct taped the foam chest cavity to an old tee shirt and then secured the surgical gown over it with hot glue. To finish up, the I mounted the retractor to the chest cavity with hot glue. I then positioned the instruments and hot glued them to the retractor. Finally, I added the Open Heart Surgery for Dummies picture and coated the chest cavity with Vaseline to add a slimy look.