Today's stethoscopes are a far-cry from a hollow tube, but for what they can accomplish, they're remarkably simple devices. In a basic acoustic stethoscope, which is still the most common type in use today, you're looking at three main sections and a total of five crucial parts [source: MyStethoscope].
Chestpiece: This is the part that contacts the patient, capturing sound. There are two sides of the chestpiece. On one side is the diaphragm, a flat, metal disc that in turn contains a flat, plastic disc. The diaphragm is the larger component of the chestpiece. On the other side is the bell, a hollow, bell-shaped piece of metal with a tiny hole on top. The bell is better at picking up low-pitch sounds, such as heart murmurs (the aforementioned "whoosh"); the diaphragm excels in the higher-pitch range, which includes normal breath sounds and heartbeats ("lub-lub") [source: IPAT].
Tubing: A Y-shaped configuration of rubber tubes runs from the chestpiece to the headset. The sounds picked up by the chestpiece initially travel through a single tube, eventually splitting into two channels as they near the headset so the listener can hear it in both ears. Stethoscope tubing typically ranges from about 18 to 27 inches (45 to 68 centimeters) long.
Headset: The rubber tubing ends at a set of metal tubes that carry the sound to the eartips in the listener's ears. The eartips are made of soft rubber, not only for comfort but also to create a seal that helps block out environmental noise.
It's not a fancy machine. The stethoscope picks up sound much as our eardrums do. The big difference is in how the sound arrives there.