couldn't hear a THING with THREE different Littmans

This weekend, I was able to try the Littman Lightweight, Classic II SE and Master Cardiology models. I have never used a stethoscope before. What I had always imagined was that I'd hear a loud, strong heartbeart. The girl at the store actually put the piece to my daughter's chest and let me listen. I am not sure what the extent of her experience was, though. She did say it would take practice to tune out the ambient sounds.

Well, I really couldn't hear anything -- not even with the Master Cardiology model. The sounds were just SOOO faint. And, yes -- I had the earpieces in the right way (facing forward). The sound I heard was similar to that sound you hear when you are underwater -- when sounds are muffled.

Is this normal ??? I really did not notice a different AT ALL between all three models! Is it just my inexperience???

Thanks.