A working (toy) stethoscope.
This model does work and I was able to faintly hear my own heartbeat with it but can't really see this taking off to supply the hospitals of the world...
Print either the one-piece or diaphraghm + bell and glue/acetone together. Two versions are supplied because the supports are quite hard to remove on the one piece version. I also brushed mine with acetone to plug up any holes.
Print a copy of the membrane and glue thin foil or paper to the side that isn't flat. Once dried secure the membrane inside the diaphragm with blu-tak and the foil/paper facing out.
Attach plastic tubes to the outlets on the bell. You should now have a working stethoscope, so stick the tubes in your ears and see if you can hear a heartbeat.
Openscad source file is provided so you can adjust for different size tubing, etc. The STL files assume ~1CM diameter tubes.