Doctors listen to lub-dub with a stethoscope (auscultation) because:
Listening to heart sounds is an essential skill for healthcare professionals. With a stethoscope, you can hear the lub-dub rhythm and detect any abnormalities. If you're interested in learning more about heart sounds, you can: heart sound lub dub
Imagine a two-room pump:
The “lub-dub” is the sound of your heart valves closing. Doctors listen to lub-dub with a stethoscope (auscultation)