e|lec|tro|steth|o|graph

e|lec|tro|steth|o|graph «ih _LEHK troh STEHTH uh graf, -grahf», noun.

a very sensitive, electrically operated instrument used to record sounds of the heart: »

The medical instrument is an electrostethograph, which gives doctors a high-fidelity record of heart sounds so faint they cannot be heard by the human ear even aided by a physician's stethoscope (Science News Letter).